diff --git a/deploy/python/infer.py b/deploy/python/infer.py
index c8737ccfdb5a87364ca9a4c250dd0204df5798fc..09eec1153796ae43f41f0881db22029ed6056e45 100644
--- a/deploy/python/infer.py
+++ b/deploy/python/infer.py
@@ -31,16 +31,32 @@ sys.path.insert(0, parent_path)
 
 from benchmark_utils import PaddleInferBenchmark
 from picodet_postprocess import PicoDetPostProcess
-from preprocess import preprocess, Resize, NormalizeImage, Permute, PadStride, LetterBoxResize, WarpAffine, decode_image
+from preprocess import preprocess, Resize, NormalizeImage, Permute, PadStride, LetterBoxResize, WarpAffine, Pad, decode_image
 from keypoint_preprocess import EvalAffine, TopDownEvalAffine, expand_crop
 from visualize import visualize_box_mask
 from utils import argsparser, Timer, get_current_memory_mb
 
 # Global dictionary
 SUPPORT_MODELS = {
-    'YOLO', 'RCNN', 'SSD', 'Face', 'FCOS', 'SOLOv2', 'TTFNet', 'S2ANet', 'JDE',
-    'FairMOT', 'DeepSORT', 'GFL', 'PicoDet', 'CenterNet', 'TOOD', 'RetinaNet',
-    'StrongBaseline', 'STGCN'
+    'YOLO',
+    'RCNN',
+    'SSD',
+    'Face',
+    'FCOS',
+    'SOLOv2',
+    'TTFNet',
+    'S2ANet',
+    'JDE',
+    'FairMOT',
+    'DeepSORT',
+    'GFL',
+    'PicoDet',
+    'CenterNet',
+    'TOOD',
+    'RetinaNet',
+    'StrongBaseline',
+    'STGCN',
+    'YOLOX',
 }
 
 
diff --git a/deploy/python/preprocess.py b/deploy/python/preprocess.py
index 998367a349b3e14045991c2e1d2af2e6ec94e03d..b8cf256d508e66798063ada9f62d45dbee8fca07 100644
--- a/deploy/python/preprocess.py
+++ b/deploy/python/preprocess.py
@@ -246,6 +246,81 @@ class LetterBoxResize(object):
         return im, im_info
 
 
+class Pad(object):
+    def __init__(self,
+                 size=None,
+                 size_divisor=32,
+                 pad_mode=0,
+                 offsets=None,
+                 fill_value=(127.5, 127.5, 127.5)):
+        """
+        Pad image to a specified size or multiple of size_divisor.
+        Args:
+            size (int, Sequence): image target size, if None, pad to multiple of size_divisor, default None
+            size_divisor (int): size divisor, default 32
+            pad_mode (int): pad mode, currently only supports four modes [-1, 0, 1, 2]. if -1, use specified offsets
+                if 0, only pad to right and bottom. if 1, pad according to center. if 2, only pad left and top
+            offsets (list): [offset_x, offset_y], specify offset while padding, only supported pad_mode=-1
+            fill_value (bool): rgb value of pad area, default (127.5, 127.5, 127.5)
+        """
+        super(Pad, self).__init__()
+        if isinstance(size, int):
+            size = [size, size]
+
+        assert pad_mode in [
+            -1, 0, 1, 2
+        ], 'currently only supports four modes [-1, 0, 1, 2]'
+        if pad_mode == -1:
+            assert offsets, 'if pad_mode is -1, offsets should not be None'
+
+        self.size = size
+        self.size_divisor = size_divisor
+        self.pad_mode = pad_mode
+        self.fill_value = fill_value
+        self.offsets = offsets
+
+    def apply_image(self, image, offsets, im_size, size):
+        x, y = offsets
+        im_h, im_w = im_size
+        h, w = size
+        canvas = np.ones((h, w, 3), dtype=np.float32)
+        canvas *= np.array(self.fill_value, dtype=np.float32)
+        canvas[y:y + im_h, x:x + im_w, :] = image.astype(np.float32)
+        return canvas
+
+    def __call__(self, im, im_info):
+        im_h, im_w = im.shape[:2]
+        if self.size:
+            h, w = self.size
+            assert (
+                im_h <= h and im_w <= w
+            ), '(h, w) of target size should be greater than (im_h, im_w)'
+        else:
+            h = int(np.ceil(im_h / self.size_divisor) * self.size_divisor)
+            w = int(np.ceil(im_w / self.size_divisor) * self.size_divisor)
+
+        if h == im_h and w == im_w:
+            im = im.astype(np.float32)
+            return im, im_info
+
+        if self.pad_mode == -1:
+            offset_x, offset_y = self.offsets
+        elif self.pad_mode == 0:
+            offset_y, offset_x = 0, 0
+        elif self.pad_mode == 1:
+            offset_y, offset_x = (h - im_h) // 2, (w - im_w) // 2
+        else:
+            offset_y, offset_x = h - im_h, w - im_w
+
+        offsets, im_size, size = [offset_x, offset_y], [im_h, im_w], [h, w]
+        im = self.apply_image(im, offsets, im_size, size)
+
+        if self.pad_mode == 0:
+            return im, im_info
+
+        return im, im_info
+
+
 class WarpAffine(object):
     """Warp affine the image
     """
diff --git a/ppdet/data/source/dataset.py b/ppdet/data/source/dataset.py
index e086dc97d3029356fc1865ae8b46f94ea21a75a0..b8193c1c92eb47f26db27e9fd601c1c657e8dd63 100644
--- a/ppdet/data/source/dataset.py
+++ b/ppdet/data/source/dataset.py
@@ -5,7 +5,7 @@
 # You may obtain a copy of the License at   
 #   
 #     http://www.apache.org/licenses/LICENSE-2.0    
-#   
+# 
 # Unless required by applicable law or agreed to in writing, software   
 # distributed under the License is distributed on an "AS IS" BASIS, 
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  
@@ -75,7 +75,7 @@ class DetDataset(Dataset):
             n = len(self.roidbs)
             roidb = [roidb, ] + [
                 copy.deepcopy(self.roidbs[np.random.randint(n)])
-                for _ in range(3)
+                for _ in range(4)
             ]
         if isinstance(roidb, Sequence):
             for r in roidb:
diff --git a/ppdet/data/transform/operators.py b/ppdet/data/transform/operators.py
index 7eae8db0ba67a87a1337bd4a289d505aee365aaa..c3fb37e262d327234f505a6fe8bb681ad1894fcb 100644
--- a/ppdet/data/transform/operators.py
+++ b/ppdet/data/transform/operators.py
@@ -2034,13 +2034,14 @@ class Pad(BaseOperator):
         if self.size:
             h, w = self.size
             assert (
-                im_h < h and im_w < w
+                im_h <= h and im_w <= w
             ), '(h, w) of target size should be greater than (im_h, im_w)'
         else:
             h = int(np.ceil(im_h / self.size_divisor) * self.size_divisor)
             w = int(np.ceil(im_w / self.size_divisor) * self.size_divisor)
 
         if h == im_h and w == im_w:
+            sample['image'] = im.astype(np.float32)
             return sample
 
         if self.pad_mode == -1:
@@ -2139,16 +2140,29 @@ class Rbox2Poly(BaseOperator):
 
 @register_op
 class AugmentHSV(BaseOperator):
-    def __init__(self, fraction=0.50, is_bgr=True):
-        """ 
-        Augment the SV channel of image data.
-        Args:
-            fraction (float): the fraction for augment. Default: 0.5.
-            is_bgr (bool): whether the image is BGR mode. Default: True.
-        """
+    """ 
+    Augment the SV channel of image data.
+    Args:
+        fraction (float): the fraction for augment. Default: 0.5.
+        is_bgr (bool): whether the image is BGR mode. Default: True.
+        hgain (float): H channel gains
+        sgain (float): S channel gains
+        vgain (float): V channel gains
+    """
+
+    def __init__(self,
+                 fraction=0.50,
+                 is_bgr=True,
+                 hgain=None,
+                 sgain=None,
+                 vgain=None):
         super(AugmentHSV, self).__init__()
         self.fraction = fraction
         self.is_bgr = is_bgr
+        self.hgain = hgain
+        self.sgain = sgain
+        self.vgain = vgain
+        self.use_hsvgain = False if hgain is None else True
 
     def apply(self, sample, context=None):
         img = sample['image']
@@ -2156,21 +2170,33 @@ class AugmentHSV(BaseOperator):
             img_hsv = cv2.cvtColor(img, cv2.COLOR_BGR2HSV)
         else:
             img_hsv = cv2.cvtColor(img, cv2.COLOR_RGB2HSV)
-        S = img_hsv[:, :, 1].astype(np.float32)
-        V = img_hsv[:, :, 2].astype(np.float32)
 
-        a = (random.random() * 2 - 1) * self.fraction + 1
-        S *= a
-        if a > 1:
-            np.clip(S, a_min=0, a_max=255, out=S)
+        if self.use_hsvgain:
+            hsv_augs = np.random.uniform(
+                -1, 1, 3) * [self.hgain, self.sgain, self.vgain]
+            # random selection of h, s, v
+            hsv_augs *= np.random.randint(0, 2, 3)
+            img_hsv[..., 0] = (img_hsv[..., 0] + hsv_augs[0]) % 180
+            img_hsv[..., 1] = np.clip(img_hsv[..., 1] + hsv_augs[1], 0, 255)
+            img_hsv[..., 2] = np.clip(img_hsv[..., 2] + hsv_augs[2], 0, 255)
 
-        a = (random.random() * 2 - 1) * self.fraction + 1
-        V *= a
-        if a > 1:
-            np.clip(V, a_min=0, a_max=255, out=V)
+        else:
+            S = img_hsv[:, :, 1].astype(np.float32)
+            V = img_hsv[:, :, 2].astype(np.float32)
+
+            a = (random.random() * 2 - 1) * self.fraction + 1
+            S *= a
+            if a > 1:
+                np.clip(S, a_min=0, a_max=255, out=S)
+
+            a = (random.random() * 2 - 1) * self.fraction + 1
+            V *= a
+            if a > 1:
+                np.clip(V, a_min=0, a_max=255, out=V)
+
+            img_hsv[:, :, 1] = S.astype(np.uint8)
+            img_hsv[:, :, 2] = V.astype(np.uint8)
 
-        img_hsv[:, :, 1] = S.astype(np.uint8)
-        img_hsv[:, :, 2] = V.astype(np.uint8)
         if self.is_bgr:
             cv2.cvtColor(img_hsv, cv2.COLOR_HSV2BGR, dst=img)
         else:
@@ -3018,3 +3044,373 @@ class CenterRandColor(BaseOperator):
             img = func(img, img_gray)
         sample['image'] = img
         return sample
+
+
+@register_op
+class Mosaic(BaseOperator):
+    """ Mosaic operator for image and gt_bboxes
+    The code is based on https://github.com/Megvii-BaseDetection/YOLOX/blob/main/yolox/data/datasets/mosaicdetection.py
+
+    1. get mosaic coords
+    2. clip bbox and get mosaic_labels
+    3. random_affine augment
+    4. Mixup augment as copypaste (optinal), not used in tiny/nano
+
+    Args:
+        prob (float): probability of using Mosaic, 1.0 as default
+        input_dim (list[int]): input shape
+        degrees (list[2]): the rotate range to apply, transform range is [min, max]
+        translate (list[2]): the translate range to apply, transform range is [min, max]
+        scale (list[2]): the scale range to apply, transform range is [min, max]
+        shear (list[2]): the shear range to apply, transform range is [min, max]
+        enable_mixup (bool): whether to enable Mixup or not
+        mixup_prob (float): probability of using Mixup, 1.0 as default
+        mixup_scale (list[int]): scale range of Mixup
+        remove_outside_box (bool): whether remove outside boxes, False as
+            default in COCO dataset, True in MOT dataset
+    """
+
+    def __init__(self,
+                 prob=1.0,
+                 input_dim=[640, 640],
+                 degrees=[-10, 10],
+                 translate=[-0.1, 0.1],
+                 scale=[0.1, 2],
+                 shear=[-2, 2],
+                 enable_mixup=True,
+                 mixup_prob=1.0,
+                 mixup_scale=[0.5, 1.5],
+                 remove_outside_box=False):
+        super(Mosaic, self).__init__()
+        self.prob = prob
+        self.input_dim = input_dim
+        self.degrees = degrees
+        self.translate = translate
+        self.scale = scale
+        self.shear = shear
+        self.enable_mixup = enable_mixup
+        self.mixup_prob = mixup_prob
+        self.mixup_scale = mixup_scale
+        self.remove_outside_box = remove_outside_box
+
+    def get_mosaic_coords(self, mosaic_idx, xc, yc, w, h, input_h, input_w):
+        # (x1, y1, x2, y2) means coords in large image,
+        # small_coords means coords in small image in mosaic aug.
+        if mosaic_idx == 0:
+            # top left
+            x1, y1, x2, y2 = max(xc - w, 0), max(yc - h, 0), xc, yc
+            small_coords = w - (x2 - x1), h - (y2 - y1), w, h
+        elif mosaic_idx == 1:
+            # top right
+            x1, y1, x2, y2 = xc, max(yc - h, 0), min(xc + w, input_w * 2), yc
+            small_coords = 0, h - (y2 - y1), min(w, x2 - x1), h
+        elif mosaic_idx == 2:
+            # bottom left
+            x1, y1, x2, y2 = max(xc - w, 0), yc, xc, min(input_h * 2, yc + h)
+            small_coords = w - (x2 - x1), 0, w, min(y2 - y1, h)
+        elif mosaic_idx == 3:
+            # bottom right
+            x1, y1, x2, y2 = xc, yc, min(xc + w, input_w * 2), min(input_h * 2,
+                                                                   yc + h)
+            small_coords = 0, 0, min(w, x2 - x1), min(y2 - y1, h)
+
+        return (x1, y1, x2, y2), small_coords
+
+    def random_affine_augment(self,
+                              img,
+                              labels=[],
+                              input_dim=[640, 640],
+                              degrees=[-10, 10],
+                              scales=[0.1, 2],
+                              shears=[-2, 2],
+                              translates=[-0.1, 0.1]):
+        # random rotation and scale
+        degree = random.uniform(degrees[0], degrees[1])
+        scale = random.uniform(scales[0], scales[1])
+        assert scale > 0, "Argument scale should be positive."
+        R = cv2.getRotationMatrix2D(angle=degree, center=(0, 0), scale=scale)
+        M = np.ones([2, 3])
+
+        # random shear
+        shear = random.uniform(shears[0], shears[1])
+        shear_x = math.tan(shear * math.pi / 180)
+        shear_y = math.tan(shear * math.pi / 180)
+        M[0] = R[0] + shear_y * R[1]
+        M[1] = R[1] + shear_x * R[0]
+
+        # random translation
+        translate = random.uniform(translates[0], translates[1])
+        translation_x = translate * input_dim[0]
+        translation_y = translate * input_dim[1]
+        M[0, 2] = translation_x
+        M[1, 2] = translation_y
+
+        # warpAffine
+        img = cv2.warpAffine(
+            img, M, dsize=input_dim, borderValue=(114, 114, 114))
+
+        num_gts = len(labels)
+        if num_gts > 0:
+            # warp corner points
+            corner_points = np.ones((4 * num_gts, 3))
+            corner_points[:, :2] = labels[:, [0, 1, 2, 3, 0, 3, 2, 1]].reshape(
+                4 * num_gts, 2)  # x1y1, x2y2, x1y2, x2y1
+            # apply affine transform
+            corner_points = corner_points @M.T
+            corner_points = corner_points.reshape(num_gts, 8)
+
+            # create new boxes
+            corner_xs = corner_points[:, 0::2]
+            corner_ys = corner_points[:, 1::2]
+            new_bboxes = np.concatenate((corner_xs.min(1), corner_ys.min(1),
+                                         corner_xs.max(1), corner_ys.max(1)))
+            new_bboxes = new_bboxes.reshape(4, num_gts).T
+
+            # clip boxes
+            new_bboxes[:, 0::2] = np.clip(new_bboxes[:, 0::2], 0, input_dim[0])
+            new_bboxes[:, 1::2] = np.clip(new_bboxes[:, 1::2], 0, input_dim[1])
+            labels[:, :4] = new_bboxes
+
+        return img, labels
+
+    def __call__(self, sample, context=None):
+        if not isinstance(sample, Sequence):
+            return sample
+
+        assert len(
+            sample) == 5, "Mosaic needs 5 samples, 4 for mosaic and 1 for mixup."
+        if np.random.uniform(0., 1.) > self.prob:
+            return sample[0]
+
+        mosaic_gt_bbox, mosaic_gt_class, mosaic_is_crowd = [], [], []
+        input_h, input_w = self.input_dim
+        yc = int(random.uniform(0.5 * input_h, 1.5 * input_h))
+        xc = int(random.uniform(0.5 * input_w, 1.5 * input_w))
+        mosaic_img = np.full((input_h * 2, input_w * 2, 3), 114, dtype=np.uint8)
+
+        # 1. get mosaic coords
+        for mosaic_idx, sp in enumerate(sample[:4]):
+            img = sp['image']
+            gt_bbox = sp['gt_bbox']
+            h0, w0 = img.shape[:2]
+            scale = min(1. * input_h / h0, 1. * input_w / w0)
+            img = cv2.resize(
+                img, (int(w0 * scale), int(h0 * scale)),
+                interpolation=cv2.INTER_LINEAR)
+            (h, w, c) = img.shape[:3]
+
+            # suffix l means large image, while s means small image in mosaic aug.
+            (l_x1, l_y1, l_x2, l_y2), (
+                s_x1, s_y1, s_x2, s_y2) = self.get_mosaic_coords(
+                    mosaic_idx, xc, yc, w, h, input_h, input_w)
+
+            mosaic_img[l_y1:l_y2, l_x1:l_x2] = img[s_y1:s_y2, s_x1:s_x2]
+            padw, padh = l_x1 - s_x1, l_y1 - s_y1
+
+            # Normalized xywh to pixel xyxy format
+            _gt_bbox = gt_bbox.copy()
+            if len(gt_bbox) > 0:
+                _gt_bbox[:, 0] = scale * gt_bbox[:, 0] + padw
+                _gt_bbox[:, 1] = scale * gt_bbox[:, 1] + padh
+                _gt_bbox[:, 2] = scale * gt_bbox[:, 2] + padw
+                _gt_bbox[:, 3] = scale * gt_bbox[:, 3] + padh
+
+            mosaic_gt_bbox.append(_gt_bbox)
+            mosaic_gt_class.append(sp['gt_class'])
+            mosaic_is_crowd.append(sp['is_crowd'])
+
+        # 2. clip bbox and get mosaic_labels([gt_bbox, gt_class, is_crowd])
+        if len(mosaic_gt_bbox):
+            mosaic_gt_bbox = np.concatenate(mosaic_gt_bbox, 0)
+            mosaic_gt_class = np.concatenate(mosaic_gt_class, 0)
+            mosaic_is_crowd = np.concatenate(mosaic_is_crowd, 0)
+            mosaic_labels = np.concatenate([
+                mosaic_gt_bbox, mosaic_gt_class.astype(mosaic_gt_bbox.dtype),
+                mosaic_is_crowd.astype(mosaic_gt_bbox.dtype)
+            ], 1)
+            if self.remove_outside_box:
+                # for MOT dataset
+                flag1 = mosaic_gt_bbox[:, 0] < 2 * input_w
+                flag2 = mosaic_gt_bbox[:, 2] > 0
+                flag3 = mosaic_gt_bbox[:, 1] < 2 * input_h
+                flag4 = mosaic_gt_bbox[:, 3] > 0
+                flag_all = flag1 * flag2 * flag3 * flag4
+                mosaic_labels = mosaic_labels[flag_all]
+            else:
+                mosaic_labels[:, 0] = np.clip(mosaic_labels[:, 0], 0,
+                                              2 * input_w)
+                mosaic_labels[:, 1] = np.clip(mosaic_labels[:, 1], 0,
+                                              2 * input_h)
+                mosaic_labels[:, 2] = np.clip(mosaic_labels[:, 2], 0,
+                                              2 * input_w)
+                mosaic_labels[:, 3] = np.clip(mosaic_labels[:, 3], 0,
+                                              2 * input_h)
+        else:
+            mosaic_labels = np.zeros((1, 6))
+
+        # 3. random_affine augment
+        mosaic_img, mosaic_labels = self.random_affine_augment(
+            mosaic_img,
+            mosaic_labels,
+            input_dim=self.input_dim,
+            degrees=self.degrees,
+            translates=self.translate,
+            scales=self.scale,
+            shears=self.shear)
+
+        # 4. Mixup augment as copypaste, https://arxiv.org/abs/2012.07177
+        # optinal, not used(enable_mixup=False) in tiny/nano
+        if (self.enable_mixup and not len(mosaic_labels) == 0 and
+                random.random() < self.mixup_prob):
+            sample_mixup = sample[4]
+            mixup_img = sample_mixup['image']
+            cp_labels = np.concatenate([
+                sample_mixup['gt_bbox'],
+                sample_mixup['gt_class'].astype(mosaic_labels.dtype),
+                sample_mixup['is_crowd'].astype(mosaic_labels.dtype)
+            ], 1)
+            mosaic_img, mosaic_labels = self.mixup_augment(
+                mosaic_img, mosaic_labels, self.input_dim, cp_labels, mixup_img)
+
+        sample0 = sample[0]
+        sample0['image'] = mosaic_img.astype(np.uint8)  # can not be float32
+        sample0['h'] = float(mosaic_img.shape[0])
+        sample0['w'] = float(mosaic_img.shape[1])
+        sample0['im_shape'][0] = sample0['h']
+        sample0['im_shape'][1] = sample0['w']
+        sample0['gt_bbox'] = mosaic_labels[:, :4].astype(np.float32)
+        sample0['gt_class'] = mosaic_labels[:, 4:5].astype(np.float32)
+        sample0['is_crowd'] = mosaic_labels[:, 5:6].astype(np.float32)
+        return sample0
+
+    def mixup_augment(self, origin_img, origin_labels, input_dim, cp_labels,
+                      img):
+        jit_factor = random.uniform(*self.mixup_scale)
+        FLIP = random.uniform(0, 1) > 0.5
+        if len(img.shape) == 3:
+            cp_img = np.ones(
+                (input_dim[0], input_dim[1], 3), dtype=np.uint8) * 114
+        else:
+            cp_img = np.ones(input_dim, dtype=np.uint8) * 114
+
+        cp_scale_ratio = min(input_dim[0] / img.shape[0],
+                             input_dim[1] / img.shape[1])
+        resized_img = cv2.resize(
+            img, (int(img.shape[1] * cp_scale_ratio),
+                  int(img.shape[0] * cp_scale_ratio)),
+            interpolation=cv2.INTER_LINEAR)
+
+        cp_img[:int(img.shape[0] * cp_scale_ratio), :int(img.shape[
+            1] * cp_scale_ratio)] = resized_img
+
+        cp_img = cv2.resize(cp_img, (int(cp_img.shape[1] * jit_factor),
+                                     int(cp_img.shape[0] * jit_factor)))
+        cp_scale_ratio *= jit_factor
+
+        if FLIP:
+            cp_img = cp_img[:, ::-1, :]
+
+        origin_h, origin_w = cp_img.shape[:2]
+        target_h, target_w = origin_img.shape[:2]
+        padded_img = np.zeros(
+            (max(origin_h, target_h), max(origin_w, target_w), 3),
+            dtype=np.uint8)
+        padded_img[:origin_h, :origin_w] = cp_img
+
+        x_offset, y_offset = 0, 0
+        if padded_img.shape[0] > target_h:
+            y_offset = random.randint(0, padded_img.shape[0] - target_h - 1)
+        if padded_img.shape[1] > target_w:
+            x_offset = random.randint(0, padded_img.shape[1] - target_w - 1)
+        padded_cropped_img = padded_img[y_offset:y_offset + target_h, x_offset:
+                                        x_offset + target_w]
+
+        # adjust boxes
+        cp_bboxes_origin_np = cp_labels[:, :4].copy()
+        cp_bboxes_origin_np[:, 0::2] = np.clip(cp_bboxes_origin_np[:, 0::2] *
+                                               cp_scale_ratio, 0, origin_w)
+        cp_bboxes_origin_np[:, 1::2] = np.clip(cp_bboxes_origin_np[:, 1::2] *
+                                               cp_scale_ratio, 0, origin_h)
+
+        if FLIP:
+            cp_bboxes_origin_np[:, 0::2] = (
+                origin_w - cp_bboxes_origin_np[:, 0::2][:, ::-1])
+        cp_bboxes_transformed_np = cp_bboxes_origin_np.copy()
+        if self.remove_outside_box:
+            # for MOT dataset
+            cp_bboxes_transformed_np[:, 0::2] -= x_offset
+            cp_bboxes_transformed_np[:, 1::2] -= y_offset
+        else:
+            cp_bboxes_transformed_np[:, 0::2] = np.clip(
+                cp_bboxes_transformed_np[:, 0::2] - x_offset, 0, target_w)
+            cp_bboxes_transformed_np[:, 1::2] = np.clip(
+                cp_bboxes_transformed_np[:, 1::2] - y_offset, 0, target_h)
+
+        cls_labels = cp_labels[:, 4:5].copy()
+        crd_labels = cp_labels[:, 5:6].copy()
+        box_labels = cp_bboxes_transformed_np
+        labels = np.hstack((box_labels, cls_labels, crd_labels))
+        if self.remove_outside_box:
+            labels = labels[labels[:, 0] < target_w]
+            labels = labels[labels[:, 2] > 0]
+            labels = labels[labels[:, 1] < target_h]
+            labels = labels[labels[:, 3] > 0]
+
+        origin_labels = np.vstack((origin_labels, labels))
+        origin_img = origin_img.astype(np.float32)
+        origin_img = 0.5 * origin_img + 0.5 * padded_cropped_img.astype(
+            np.float32)
+
+        return origin_img.astype(np.uint8), origin_labels
+
+
+@register_op
+class PadResize(BaseOperator):
+    """ PadResize for image and gt_bbbox
+
+    Args:
+        target_size (list[int]): input shape
+        fill_value (float): pixel value of padded image
+    """
+
+    def __init__(self, target_size, fill_value=114):
+        super(PadResize, self).__init__()
+        if isinstance(target_size, Integral):
+            target_size = [target_size, target_size]
+        self.target_size = target_size
+        self.fill_value = fill_value
+
+    def _resize(self, img, bboxes, labels):
+        ratio = min(self.target_size[0] / img.shape[0],
+                    self.target_size[1] / img.shape[1])
+        w, h = int(img.shape[1] * ratio), int(img.shape[0] * ratio)
+        resized_img = cv2.resize(img, (w, h), interpolation=cv2.INTER_LINEAR)
+
+        if len(bboxes) > 0:
+            bboxes *= ratio
+            mask = np.minimum(bboxes[:, 2] - bboxes[:, 0],
+                              bboxes[:, 3] - bboxes[:, 1]) > 1
+            bboxes = bboxes[mask]
+            labels = labels[mask]
+        return resized_img, bboxes, labels
+
+    def _pad(self, img):
+        h, w, _ = img.shape
+        if h == self.target_size[0] and w == self.target_size[1]:
+            return img
+        padded_img = np.full(
+            (self.target_size[0], self.target_size[1], 3),
+            self.fill_value,
+            dtype=np.uint8)
+        padded_img[:h, :w] = img
+        return padded_img
+
+    def apply(self, sample, context=None):
+        image = sample['image']
+        bboxes = sample['gt_bbox']
+        labels = sample['gt_class']
+        image, bboxes, labels = self._resize(image, bboxes, labels)
+        sample['image'] = self._pad(image).astype(np.float32)
+        sample['gt_bbox'] = bboxes
+        sample['gt_class'] = labels
+        return sample
diff --git a/ppdet/engine/export_utils.py b/ppdet/engine/export_utils.py
index bddb4af07ca91f5b82389fdeba39ba77c1a1344e..12fb1ea6ffe369fef21274eb9a5221cf4e221812 100644
--- a/ppdet/engine/export_utils.py
+++ b/ppdet/engine/export_utils.py
@@ -48,6 +48,7 @@ TRT_MIN_SUBGRAPH = {
     'PicoDet': 3,
     'CenterNet': 5,
     'TOOD': 5,
+    'YOLOX': 8,
 }
 
 KEYPOINT_ARCH = ['HigherHRNet', 'TopDownHRNet']
@@ -147,6 +148,12 @@ def _dump_infer_config(config, path, image_shape, model):
             infer_cfg['min_subgraph_size'] = min_subgraph_size
             arch_state = True
             break
+
+    if infer_arch == 'YOLOX':
+        infer_cfg['arch'] = infer_arch
+        infer_cfg['min_subgraph_size'] = TRT_MIN_SUBGRAPH[infer_arch]
+        arch_state = True
+
     if not arch_state:
         logger.error(
             'Architecture: {} is not supported for exporting model now.\n'.
diff --git a/ppdet/engine/trainer.py b/ppdet/engine/trainer.py
index 622b9c3b290cb53fc40c4d07341ac115e8b73922..f15b992112beef3a93158bd15e1622cf63398a33 100644
--- a/ppdet/engine/trainer.py
+++ b/ppdet/engine/trainer.py
@@ -28,6 +28,7 @@ from PIL import Image, ImageOps, ImageFile
 ImageFile.LOAD_TRUNCATED_IMAGES = True
 
 import paddle
+import paddle.nn as nn
 import paddle.distributed as dist
 from paddle.distributed import fleet
 from paddle import amp
@@ -99,6 +100,12 @@ class Trainer(object):
             self.model = self.cfg.model
             self.is_loaded_weights = True
 
+        if cfg.architecture == 'YOLOX':
+            for k, m in self.model.named_sublayers():
+                if isinstance(m, nn.BatchNorm2D):
+                    m.epsilon = 1e-3  # for amp(fp16)
+                    m.momentum = 0.97  # 0.03 in pytorch
+
         #normalize params for deploy
         if 'slim' in cfg and cfg['slim_type'] == 'OFA':
             self.model.model.load_meanstd(cfg['TestReader'][
@@ -117,10 +124,11 @@ class Trainer(object):
         if self.use_ema:
             ema_decay = self.cfg.get('ema_decay', 0.9998)
             cycle_epoch = self.cfg.get('cycle_epoch', -1)
+            ema_decay_type = self.cfg.get('ema_decay_type', 'threshold')
             self.ema = ModelEMA(
                 self.model,
                 decay=ema_decay,
-                use_thres_step=True,
+                ema_decay_type=ema_decay_type,
                 cycle_epoch=cycle_epoch)
 
         # EvalDataset build with BatchSampler to evaluate in single device
diff --git a/ppdet/modeling/architectures/__init__.py b/ppdet/modeling/architectures/__init__.py
index 71c53067f72f96c1d24da19aa4313449e91f4b95..9360a5b7b15596302ae54fc7b375e83718820da0 100644
--- a/ppdet/modeling/architectures/__init__.py
+++ b/ppdet/modeling/architectures/__init__.py
@@ -5,6 +5,13 @@
 # You may obtain a copy of the License at   
 #   
 #     http://www.apache.org/licenses/LICENSE-2.0    
+#   
+# Unless required by applicable law or agreed to in writing, software   
+# distributed under the License is distributed on an "AS IS" BASIS, 
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  
+# See the License for the specific language governing permissions and   
+# limitations under the License.
+
 from . import meta_arch
 from . import faster_rcnn
 from . import mask_rcnn
@@ -28,6 +35,7 @@ from . import sparse_rcnn
 from . import tood
 from . import retinanet
 from . import bytetrack
+from . import yolox
 
 from .meta_arch import *
 from .faster_rcnn import *
@@ -53,3 +61,4 @@ from .sparse_rcnn import *
 from .tood import *
 from .retinanet import *
 from .bytetrack import *
+from .yolox import *
diff --git a/ppdet/modeling/architectures/yolox.py b/ppdet/modeling/architectures/yolox.py
new file mode 100644
index 0000000000000000000000000000000000000000..5965473e793fcbfa580be8fb18a14b7a1c950305
--- /dev/null
+++ b/ppdet/modeling/architectures/yolox.py
@@ -0,0 +1,144 @@
+# Copyright (c) 2022 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+
+from ppdet.core.workspace import register, create
+from .meta_arch import BaseArch
+
+import random
+import paddle
+import paddle.nn.functional as F
+import paddle.distributed as dist
+from ppdet.modeling.ops import paddle_distributed_is_initialized
+
+__all__ = ['YOLOX']
+
+
+@register
+class YOLOX(BaseArch):
+    """
+    YOLOX network, see https://arxiv.org/abs/2107.08430
+
+    Args:
+        backbone (nn.Layer): backbone instance
+        neck (nn.Layer): neck instance
+        head (nn.Layer): head instance
+        for_mot (bool): whether used for MOT or not
+        input_size (list[int]): initial scale, will be reset by self._preprocess()
+        size_stride (int): stride of the size range
+        size_range (list[int]): multi-scale range for training
+        random_interval (int): interval of iter to change self._input_size
+    """
+    __category__ = 'architecture'
+
+    def __init__(self,
+                 backbone='CSPDarkNet',
+                 neck='YOLOCSPPAN',
+                 head='YOLOXHead',
+                 for_mot=False,
+                 input_size=[640, 640],
+                 size_stride=32,
+                 size_range=[15, 25],
+                 random_interval=10):
+        super(YOLOX, self).__init__()
+        self.backbone = backbone
+        self.neck = neck
+        self.head = head
+        self.for_mot = for_mot
+
+        self.input_size = input_size
+        self._input_size = paddle.to_tensor(input_size)
+        self.size_stride = size_stride
+        self.size_range = size_range
+        self.random_interval = random_interval
+        self._step = 0
+
+    @classmethod
+    def from_config(cls, cfg, *args, **kwargs):
+        # backbone
+        backbone = create(cfg['backbone'])
+
+        # fpn
+        kwargs = {'input_shape': backbone.out_shape}
+        neck = create(cfg['neck'], **kwargs)
+
+        # head
+        kwargs = {'input_shape': neck.out_shape}
+        head = create(cfg['head'], **kwargs)
+
+        return {
+            'backbone': backbone,
+            'neck': neck,
+            "head": head,
+        }
+
+    def _forward(self):
+        if self.training:
+            self._preprocess()
+        body_feats = self.backbone(self.inputs)
+        neck_feats = self.neck(body_feats, self.for_mot)
+
+        if self.training:
+            yolox_losses = self.head(neck_feats, self.inputs)
+            yolox_losses.update({'size': self._input_size[0]})
+            return yolox_losses
+        else:
+            head_outs = self.head(neck_feats)
+            bbox, bbox_num = self.head.post_process(
+                head_outs, self.inputs['im_shape'], self.inputs['scale_factor'])
+            return {'bbox': bbox, 'bbox_num': bbox_num}
+
+    def get_loss(self):
+        return self._forward()
+
+    def get_pred(self):
+        return self._forward()
+
+    def _preprocess(self):
+        # YOLOX multi-scale training, interpolate resize before inputs of the network.
+        self._get_size()
+        scale_y = self._input_size[0] / self.input_size[0]
+        scale_x = self._input_size[1] / self.input_size[1]
+        if scale_x != 1 or scale_y != 1:
+            self.inputs['image'] = F.interpolate(
+                self.inputs['image'],
+                size=self._input_size,
+                mode='bilinear',
+                align_corners=False)
+            gt_bboxes = self.inputs['gt_bbox']
+            for i in range(len(gt_bboxes)):
+                if len(gt_bboxes[i]) > 0:
+                    gt_bboxes[i][:, 0::2] = gt_bboxes[i][:, 0::2] * scale_x
+                    gt_bboxes[i][:, 1::2] = gt_bboxes[i][:, 1::2] * scale_y
+            self.inputs['gt_bbox'] = gt_bboxes
+
+    def _get_size(self):
+        # random_interval = 10 as default, every 10 iters to change self._input_size
+        image_ratio = self.input_size[1] * 1.0 / self.input_size[0]
+        if self._step % self.random_interval == 0:
+            size_factor = random.randint(*self.size_range)
+            size = [
+                self.size_stride * size_factor,
+                self.size_stride * int(size_factor * image_ratio)
+            ]
+            size = paddle.to_tensor(size)
+            if dist.get_world_size() > 1 and paddle_distributed_is_initialized(
+            ):
+                dist.barrier()
+                dist.broadcast(size, 0)
+            self._input_size = size
+        self._step += 1
diff --git a/ppdet/modeling/assigners/utils.py b/ppdet/modeling/assigners/utils.py
index 0c5e1d94fc06dd2abdf135638f9b17c8ba2ff8cf..f2d9be99509b62d585a9f4db999818b6d25a2d94 100644
--- a/ppdet/modeling/assigners/utils.py
+++ b/ppdet/modeling/assigners/utils.py
@@ -115,7 +115,7 @@ def check_points_inside_bboxes(points,
     Args:
         points (Tensor, float32): shape[L, 2], "xy" format, L: num_anchors
         bboxes (Tensor, float32): shape[B, n, 4], "xmin, ymin, xmax, ymax" format
-        center_radius_tensor (Tensor, float32): shape [L, 1] Default: None.
+        center_radius_tensor (Tensor, float32): shape [L, 1]. Default: None.
         eps (float): Default: 1e-9
     Returns:
         is_in_bboxes (Tensor, float32): shape[B, n, L], value=1. means selected
@@ -123,25 +123,28 @@ def check_points_inside_bboxes(points,
     points = points.unsqueeze([0, 1])
     x, y = points.chunk(2, axis=-1)
     xmin, ymin, xmax, ymax = bboxes.unsqueeze(2).chunk(4, axis=-1)
-    if center_radius_tensor is not None:
-        center_radius_tensor = center_radius_tensor.unsqueeze([0, 1])
-        bboxes_cx = (xmin + xmax) / 2.
-        bboxes_cy = (ymin + ymax) / 2.
-        xmin_sampling = bboxes_cx - center_radius_tensor
-        ymin_sampling = bboxes_cy - center_radius_tensor
-        xmax_sampling = bboxes_cx + center_radius_tensor
-        ymax_sampling = bboxes_cy + center_radius_tensor
-
-        xmin = paddle.maximum(xmin, xmin_sampling)
-        ymin = paddle.maximum(ymin, ymin_sampling)
-        xmax = paddle.minimum(xmax, xmax_sampling)
-        ymax = paddle.minimum(ymax, ymax_sampling)
+    # check whether `points` is in `bboxes`
     l = x - xmin
     t = y - ymin
     r = xmax - x
     b = ymax - y
-    bbox_ltrb = paddle.concat([l, t, r, b], axis=-1)
-    return (bbox_ltrb.min(axis=-1) > eps).astype(bboxes.dtype)
+    delta_ltrb = paddle.concat([l, t, r, b], axis=-1)
+    is_in_bboxes = (delta_ltrb.min(axis=-1) > eps)
+    if center_radius_tensor is not None:
+        # check whether `points` is in `center_radius`
+        center_radius_tensor = center_radius_tensor.unsqueeze([0, 1])
+        cx = (xmin + xmax) * 0.5
+        cy = (ymin + ymax) * 0.5
+        l = x - (cx - center_radius_tensor)
+        t = y - (cy - center_radius_tensor)
+        r = (cx + center_radius_tensor) - x
+        b = (cy + center_radius_tensor) - y
+        delta_ltrb_c = paddle.concat([l, t, r, b], axis=-1)
+        is_in_center = (delta_ltrb_c.min(axis=-1) > eps)
+        return (paddle.logical_and(is_in_bboxes, is_in_center),
+                paddle.logical_or(is_in_bboxes, is_in_center))
+
+    return is_in_bboxes.astype(bboxes.dtype)
 
 
 def compute_max_iou_anchor(ious):
diff --git a/ppdet/modeling/backbones/__init__.py b/ppdet/modeling/backbones/__init__.py
index bbc696dbacd048ce0ca752580ecfc54e11a1433f..e619e7ec663d8df745e690de8dc83a2c8391d7bc 100644
--- a/ppdet/modeling/backbones/__init__.py
+++ b/ppdet/modeling/backbones/__init__.py
@@ -1,15 +1,15 @@
-# copyright (c) 2020 PaddlePaddle Authors. All Rights Reserve.
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#    http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
+# Copyright (c) 2020 PaddlePaddle Authors. All Rights Reserved. 
+#   
+# Licensed under the Apache License, Version 2.0 (the "License");   
+# you may not use this file except in compliance with the License.  
+# You may obtain a copy of the License at   
+#   
+#     http://www.apache.org/licenses/LICENSE-2.0    
+# 
+# Unless required by applicable law or agreed to in writing, software   
+# distributed under the License is distributed on an "AS IS" BASIS, 
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  
+# See the License for the specific language governing permissions and   
 # limitations under the License.
 
 from . import vgg
@@ -30,6 +30,7 @@ from . import lcnet
 from . import hardnet
 from . import esnet
 from . import cspresnet
+from . import csp_darknet
 
 from .vgg import *
 from .resnet import *
@@ -49,3 +50,4 @@ from .lcnet import *
 from .hardnet import *
 from .esnet import *
 from .cspresnet import *
+from .csp_darknet import *
diff --git a/ppdet/modeling/backbones/csp_darknet.py b/ppdet/modeling/backbones/csp_darknet.py
new file mode 100644
index 0000000000000000000000000000000000000000..45b06076044b53f9f75516e38d1c52d18b1d885b
--- /dev/null
+++ b/ppdet/modeling/backbones/csp_darknet.py
@@ -0,0 +1,403 @@
+# Copyright (c) 2022 PaddlePaddle Authors. All Rights Reserved. 
+#   
+# Licensed under the Apache License, Version 2.0 (the "License");   
+# you may not use this file except in compliance with the License.  
+# You may obtain a copy of the License at   
+#   
+#     http://www.apache.org/licenses/LICENSE-2.0    
+# 
+# Unless required by applicable law or agreed to in writing, software   
+# distributed under the License is distributed on an "AS IS" BASIS, 
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  
+# See the License for the specific language governing permissions and   
+# limitations under the License.
+
+import paddle
+import paddle.nn as nn
+import paddle.nn.functional as F
+from paddle import ParamAttr
+from paddle.regularizer import L2Decay
+from ppdet.core.workspace import register, serializable
+from ppdet.modeling.ops import get_activation
+from ppdet.modeling.initializer import conv_init_
+from ..shape_spec import ShapeSpec
+
+__all__ = [
+    'CSPDarkNet', 'BaseConv', 'DWConv', 'BottleNeck', 'SPPLayer', 'SPPFLayer'
+]
+
+
+class BaseConv(nn.Layer):
+    def __init__(self,
+                 in_channels,
+                 out_channels,
+                 ksize,
+                 stride,
+                 groups=1,
+                 bias=False,
+                 act="silu"):
+        super(BaseConv, self).__init__()
+        self.conv = nn.Conv2D(
+            in_channels,
+            out_channels,
+            kernel_size=ksize,
+            stride=stride,
+            padding=(ksize - 1) // 2,
+            groups=groups,
+            bias_attr=bias)
+        self.bn = nn.BatchNorm2D(
+            out_channels,
+            weight_attr=ParamAttr(regularizer=L2Decay(0.0)),
+            bias_attr=ParamAttr(regularizer=L2Decay(0.0)))
+        self.act = get_activation(act)
+
+        self._init_weights()
+
+    def _init_weights(self):
+        conv_init_(self.conv)
+
+    def forward(self, x):
+        return self.act(self.bn(self.conv(x)))
+
+
+class DWConv(nn.Layer):
+    """Depthwise Conv"""
+
+    def __init__(self,
+                 in_channels,
+                 out_channels,
+                 ksize,
+                 stride=1,
+                 bias=False,
+                 act="silu"):
+        super(DWConv, self).__init__()
+        self.dw_conv = BaseConv(
+            in_channels,
+            in_channels,
+            ksize=ksize,
+            stride=stride,
+            groups=in_channels,
+            bias=bias,
+            act=act, )
+        self.pw_conv = BaseConv(
+            in_channels,
+            out_channels,
+            ksize=1,
+            stride=1,
+            groups=1,
+            bias=bias,
+            act=act)
+
+    def forward(self, x):
+        return self.pw_conv(self.dw_conv(x))
+
+
+class Focus(nn.Layer):
+    """Focus width and height information into channel space, used in YOLOX."""
+
+    def __init__(self,
+                 in_channels,
+                 out_channels,
+                 ksize=3,
+                 stride=1,
+                 bias=False,
+                 act="silu"):
+        super(Focus, self).__init__()
+        self.conv = BaseConv(
+            in_channels * 4,
+            out_channels,
+            ksize=ksize,
+            stride=stride,
+            bias=bias,
+            act=act)
+
+    def forward(self, inputs):
+        # inputs [bs, C, H, W] -> outputs [bs, 4C, W/2, H/2]
+        top_left = inputs[:, :, 0::2, 0::2]
+        top_right = inputs[:, :, 0::2, 1::2]
+        bottom_left = inputs[:, :, 1::2, 0::2]
+        bottom_right = inputs[:, :, 1::2, 1::2]
+        outputs = paddle.concat(
+            [top_left, bottom_left, top_right, bottom_right], 1)
+        return self.conv(outputs)
+
+
+class BottleNeck(nn.Layer):
+    def __init__(self,
+                 in_channels,
+                 out_channels,
+                 shortcut=True,
+                 expansion=0.5,
+                 depthwise=False,
+                 bias=False,
+                 act="silu"):
+        super(BottleNeck, self).__init__()
+        hidden_channels = int(out_channels * expansion)
+        Conv = DWConv if depthwise else BaseConv
+        self.conv1 = BaseConv(
+            in_channels, hidden_channels, ksize=1, stride=1, bias=bias, act=act)
+        self.conv2 = Conv(
+            hidden_channels,
+            out_channels,
+            ksize=3,
+            stride=1,
+            bias=bias,
+            act=act)
+        self.add_shortcut = shortcut and in_channels == out_channels
+
+    def forward(self, x):
+        y = self.conv2(self.conv1(x))
+        if self.add_shortcut:
+            y = y + x
+        return y
+
+
+class SPPLayer(nn.Layer):
+    """Spatial Pyramid Pooling (SPP) layer used in YOLOv3-SPP and YOLOX"""
+
+    def __init__(self,
+                 in_channels,
+                 out_channels,
+                 kernel_sizes=(5, 9, 13),
+                 bias=False,
+                 act="silu"):
+        super(SPPLayer, self).__init__()
+        hidden_channels = in_channels // 2
+        self.conv1 = BaseConv(
+            in_channels, hidden_channels, ksize=1, stride=1, bias=bias, act=act)
+        self.maxpoolings = nn.LayerList([
+            nn.MaxPool2D(
+                kernel_size=ks, stride=1, padding=ks // 2)
+            for ks in kernel_sizes
+        ])
+        conv2_channels = hidden_channels * (len(kernel_sizes) + 1)
+        self.conv2 = BaseConv(
+            conv2_channels, out_channels, ksize=1, stride=1, bias=bias, act=act)
+
+    def forward(self, x):
+        x = self.conv1(x)
+        x = paddle.concat([x] + [mp(x) for mp in self.maxpoolings], axis=1)
+        x = self.conv2(x)
+        return x
+
+
+class SPPFLayer(nn.Layer):
+    """ Spatial Pyramid Pooling - Fast (SPPF) layer used in YOLOv5 by Glenn Jocher,
+        equivalent to SPP(k=(5, 9, 13))
+    """
+
+    def __init__(self,
+                 in_channels,
+                 out_channels,
+                 ksize=5,
+                 bias=False,
+                 act='silu'):
+        super(SPPFLayer, self).__init__()
+        hidden_channels = in_channels // 2
+        self.conv1 = BaseConv(
+            in_channels, hidden_channels, ksize=1, stride=1, bias=bias, act=act)
+        self.maxpooling = nn.MaxPool2D(
+            kernel_size=ksize, stride=1, padding=ksize // 2)
+        conv2_channels = hidden_channels * 4
+        self.conv2 = BaseConv(
+            conv2_channels, out_channels, ksize=1, stride=1, bias=bias, act=act)
+
+    def forward(self, x):
+        x = self.conv1(x)
+        y1 = self.maxpooling(x)
+        y2 = self.maxpooling(y1)
+        y3 = self.maxpooling(y2)
+        concats = paddle.concat([x, y1, y2, y3], axis=1)
+        out = self.conv2(concats)
+        return out
+
+
+class CSPLayer(nn.Layer):
+    """CSP (Cross Stage Partial) layer with 3 convs, named C3 in YOLOv5"""
+
+    def __init__(self,
+                 in_channels,
+                 out_channels,
+                 num_blocks=1,
+                 shortcut=True,
+                 expansion=0.5,
+                 depthwise=False,
+                 bias=False,
+                 act="silu"):
+        super(CSPLayer, self).__init__()
+        hidden_channels = int(out_channels * expansion)
+        self.conv1 = BaseConv(
+            in_channels, hidden_channels, ksize=1, stride=1, bias=bias, act=act)
+        self.conv2 = BaseConv(
+            in_channels, hidden_channels, ksize=1, stride=1, bias=bias, act=act)
+        self.bottlenecks = nn.Sequential(* [
+            BottleNeck(
+                hidden_channels,
+                hidden_channels,
+                shortcut=shortcut,
+                expansion=1.0,
+                depthwise=depthwise,
+                bias=bias,
+                act=act) for _ in range(num_blocks)
+        ])
+        self.conv3 = BaseConv(
+            hidden_channels * 2,
+            out_channels,
+            ksize=1,
+            stride=1,
+            bias=bias,
+            act=act)
+
+    def forward(self, x):
+        x_1 = self.conv1(x)
+        x_1 = self.bottlenecks(x_1)
+        x_2 = self.conv2(x)
+        x = paddle.concat([x_1, x_2], axis=1)
+        x = self.conv3(x)
+        return x
+
+
+@register
+@serializable
+class CSPDarkNet(nn.Layer):
+    """
+    CSPDarkNet backbone.
+    Args:
+        arch (str): Architecture of CSPDarkNet, from {P5, P6, X}, default as X,
+            and 'X' means used in YOLOX, 'P5/P6' means used in YOLOv5.
+        depth_mult (float): Depth multiplier, multiply number of channels in
+            each layer, default as 1.0.
+        width_mult (float): Width multiplier, multiply number of blocks in
+            CSPLayer, default as 1.0.
+        depthwise (bool): Whether to use depth-wise conv layer.
+        act (str): Activation function type, default as 'silu'.
+        return_idx (list): Index of stages whose feature maps are returned.
+    """
+
+    __shared__ = ['depth_mult', 'width_mult', 'act']
+
+    # in_channels, out_channels, num_blocks, add_shortcut, use_spp(use_sppf)
+    # 'X' means setting used in YOLOX, 'P5/P6' means setting used in YOLOv5.
+    arch_settings = {
+        'X': [[64, 128, 3, True, False], [128, 256, 9, True, False],
+              [256, 512, 9, True, False], [512, 1024, 3, False, True]],
+        'P5': [[64, 128, 3, True, False], [128, 256, 6, True, False],
+               [256, 512, 9, True, False], [512, 1024, 3, True, True]],
+        'P6': [[64, 128, 3, True, False], [128, 256, 6, True, False],
+               [256, 512, 9, True, False], [512, 768, 3, True, False],
+               [768, 1024, 3, True, True]],
+    }
+
+    def __init__(self,
+                 arch='X',
+                 depth_mult=1.0,
+                 width_mult=1.0,
+                 depthwise=False,
+                 act='silu',
+                 return_idx=[2, 3, 4]):
+        super(CSPDarkNet, self).__init__()
+        self.arch = arch
+        self.return_idx = return_idx
+        Conv = DWConv if depthwise else BaseConv
+
+        arch_setting = self.arch_settings[arch]
+        base_channels = int(arch_setting[0][0] * width_mult)
+
+        # Note: differences between the latest YOLOv5 and the original YOLOX
+        # 1. self.stem, use SPPF(in YOLOv5) or SPP(in YOLOX)
+        # 2. use SPPF(in YOLOv5) or SPP(in YOLOX)
+        # 3. put SPPF before(YOLOv5) or SPP after(YOLOX) the last cspdark block's CSPLayer
+        # 4. whether SPPF(SPP)'CSPLayer add shortcut, True in YOLOv5, False in YOLOX
+        if arch in ['P5', 'P6']:
+            # in the latest YOLOv5, use Conv stem, and SPPF (fast, only single spp kernal size)
+            self.stem = Conv(
+                3, base_channels, ksize=6, stride=2, bias=False, act=act)
+            spp_kernal_sizes = 5
+        elif arch in ['X']:
+            # in the original YOLOX, use Focus stem, and SPP (three spp kernal sizes)
+            self.stem = Focus(
+                3, base_channels, ksize=3, stride=1, bias=False, act=act)
+            spp_kernal_sizes = (5, 9, 13)
+        else:
+            raise AttributeError("Unsupported arch type: {}".format(arch))
+
+        _out_channels = [base_channels]
+        layers_num = 1
+        self.csp_dark_blocks = []
+
+        for i, (in_channels, out_channels, num_blocks, shortcut,
+                use_spp) in enumerate(arch_setting):
+            in_channels = int(in_channels * width_mult)
+            out_channels = int(out_channels * width_mult)
+            _out_channels.append(out_channels)
+            num_blocks = max(round(num_blocks * depth_mult), 1)
+            stage = []
+
+            conv_layer = self.add_sublayer(
+                'layers{}.stage{}.conv_layer'.format(layers_num, i + 1),
+                Conv(
+                    in_channels, out_channels, 3, 2, bias=False, act=act))
+            stage.append(conv_layer)
+            layers_num += 1
+
+            if use_spp and arch in ['X']:
+                # in YOLOX use SPPLayer
+                spp_layer = self.add_sublayer(
+                    'layers{}.stage{}.spp_layer'.format(layers_num, i + 1),
+                    SPPLayer(
+                        out_channels,
+                        out_channels,
+                        kernel_sizes=spp_kernal_sizes,
+                        bias=False,
+                        act=act))
+                stage.append(spp_layer)
+                layers_num += 1
+
+            csp_layer = self.add_sublayer(
+                'layers{}.stage{}.csp_layer'.format(layers_num, i + 1),
+                CSPLayer(
+                    out_channels,
+                    out_channels,
+                    num_blocks=num_blocks,
+                    shortcut=shortcut,
+                    depthwise=depthwise,
+                    bias=False,
+                    act=act))
+            stage.append(csp_layer)
+            layers_num += 1
+
+            if use_spp and arch in ['P5', 'P6']:
+                # in latest YOLOv5 use SPPFLayer instead of SPPLayer
+                sppf_layer = self.add_sublayer(
+                    'layers{}.stage{}.sppf_layer'.format(layers_num, i + 1),
+                    SPPFLayer(
+                        out_channels,
+                        out_channels,
+                        ksize=5,
+                        bias=False,
+                        act=act))
+                stage.append(sppf_layer)
+                layers_num += 1
+
+            self.csp_dark_blocks.append(nn.Sequential(*stage))
+
+        self._out_channels = [_out_channels[i] for i in self.return_idx]
+        self.strides = [[2, 4, 8, 16, 32, 64][i] for i in self.return_idx]
+
+    def forward(self, inputs):
+        x = inputs['image']
+        outputs = []
+        x = self.stem(x)
+        for i, layer in enumerate(self.csp_dark_blocks):
+            x = layer(x)
+            if i + 1 in self.return_idx:
+                outputs.append(x)
+        return outputs
+
+    @property
+    def out_shape(self):
+        return [
+            ShapeSpec(
+                channels=c, stride=s)
+            for c, s in zip(self._out_channels, self.strides)
+        ]
diff --git a/ppdet/modeling/heads/yolo_head.py b/ppdet/modeling/heads/yolo_head.py
index 7b4e9bc3353edfe42c0c35db6fb38b67de03c730..911ae8e19810f703efaca5f17430f43b090722fe 100644
--- a/ppdet/modeling/heads/yolo_head.py
+++ b/ppdet/modeling/heads/yolo_head.py
@@ -1,3 +1,17 @@
+# Copyright (c) 2020 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
 import paddle
 import paddle.nn as nn
 import paddle.nn.functional as F
@@ -5,6 +19,16 @@ from paddle import ParamAttr
 from paddle.regularizer import L2Decay
 from ppdet.core.workspace import register
 
+import math
+import numpy as np
+from ..initializer import bias_init_with_prob, constant_
+from ..backbones.csp_darknet import BaseConv, DWConv
+from ..losses import IouLoss
+from ppdet.modeling.assigners.simota_assigner import SimOTAAssigner
+from ppdet.modeling.bbox_utils import bbox_overlaps
+
+__all__ = ['YOLOv3Head', 'YOLOXHead']
+
 
 def _de_sigmoid(x, eps=1e-7):
     x = paddle.clip(x, eps, 1. / eps)
@@ -122,3 +146,259 @@ class YOLOv3Head(nn.Layer):
     @classmethod
     def from_config(cls, cfg, input_shape):
         return {'in_channels': [i.channels for i in input_shape], }
+
+
+@register
+class YOLOXHead(nn.Layer):
+    __shared__ = ['num_classes', 'width_mult', 'act']
+    __inject__ = ['assigner', 'nms']
+
+    def __init__(self,
+                 num_classes=80,
+                 width_mult=1.0,
+                 depthwise=False,
+                 in_channels=[256, 512, 1024],
+                 feat_channels=256,
+                 fpn_strides=(8, 16, 32),
+                 l1_epoch=285,
+                 act='silu',
+                 assigner=SimOTAAssigner(use_vfl=False),
+                 nms='MultiClassNMS',
+                 loss_weight={'cls': 1.0,
+                              'obj': 1.0,
+                              'iou': 5.0,
+                              'l1': 1.0}):
+        super(YOLOXHead, self).__init__()
+        self._dtype = paddle.framework.get_default_dtype()
+        self.num_classes = num_classes
+        assert len(in_channels) > 0, "in_channels length should > 0"
+        self.in_channels = in_channels
+        feat_channels = int(feat_channels * width_mult)
+        self.fpn_strides = fpn_strides
+        self.l1_epoch = l1_epoch
+        self.assigner = assigner
+        self.nms = nms
+        self.loss_weight = loss_weight
+        self.iou_loss = IouLoss(loss_weight=1.0)  # default loss_weight 2.5
+
+        ConvBlock = DWConv if depthwise else BaseConv
+
+        self.stem_conv = nn.LayerList()
+        self.conv_cls = nn.LayerList()
+        self.conv_reg = nn.LayerList()  # reg [x,y,w,h] + obj
+        for in_c in self.in_channels:
+            self.stem_conv.append(BaseConv(in_c, feat_channels, 1, 1, act=act))
+
+            self.conv_cls.append(
+                nn.Sequential(* [
+                    ConvBlock(
+                        feat_channels, feat_channels, 3, 1, act=act), ConvBlock(
+                            feat_channels, feat_channels, 3, 1, act=act),
+                    nn.Conv2D(
+                        feat_channels,
+                        self.num_classes,
+                        1,
+                        bias_attr=ParamAttr(regularizer=L2Decay(0.0)))
+                ]))
+
+            self.conv_reg.append(
+                nn.Sequential(* [
+                    ConvBlock(
+                        feat_channels, feat_channels, 3, 1, act=act),
+                    ConvBlock(
+                        feat_channels, feat_channels, 3, 1, act=act),
+                    nn.Conv2D(
+                        feat_channels,
+                        4 + 1,  # reg [x,y,w,h] + obj
+                        1,
+                        bias_attr=ParamAttr(regularizer=L2Decay(0.0)))
+                ]))
+
+        self._init_weights()
+
+    @classmethod
+    def from_config(cls, cfg, input_shape):
+        return {'in_channels': [i.channels for i in input_shape], }
+
+    def _init_weights(self):
+        bias_cls = bias_init_with_prob(0.01)
+        bias_reg = paddle.full([5], math.log(5.), dtype=self._dtype)
+        bias_reg[:2] = 0.
+        bias_reg[-1] = bias_cls
+        for cls_, reg_ in zip(self.conv_cls, self.conv_reg):
+            constant_(cls_[-1].weight)
+            constant_(cls_[-1].bias, bias_cls)
+            constant_(reg_[-1].weight)
+            reg_[-1].bias.set_value(bias_reg)
+
+    def _generate_anchor_point(self, feat_sizes, strides, offset=0.):
+        anchor_points, stride_tensor = [], []
+        num_anchors_list = []
+        for feat_size, stride in zip(feat_sizes, strides):
+            h, w = feat_size
+            x = (paddle.arange(w) + offset) * stride
+            y = (paddle.arange(h) + offset) * stride
+            y, x = paddle.meshgrid(y, x)
+            anchor_points.append(paddle.stack([x, y], axis=-1).reshape([-1, 2]))
+            stride_tensor.append(
+                paddle.full(
+                    [len(anchor_points[-1]), 1], stride, dtype=self._dtype))
+            num_anchors_list.append(len(anchor_points[-1]))
+        anchor_points = paddle.concat(anchor_points).astype(self._dtype)
+        anchor_points.stop_gradient = True
+        stride_tensor = paddle.concat(stride_tensor)
+        stride_tensor.stop_gradient = True
+        return anchor_points, stride_tensor, num_anchors_list
+
+    def forward(self, feats, targets=None):
+        assert len(feats) == len(self.fpn_strides), \
+            "The size of feats is not equal to size of fpn_strides"
+
+        feat_sizes = [[f.shape[-2], f.shape[-1]] for f in feats]
+        cls_score_list, reg_pred_list = [], []
+        obj_score_list = []
+        for i, feat in enumerate(feats):
+            feat = self.stem_conv[i](feat)
+            cls_logit = self.conv_cls[i](feat)
+            reg_pred = self.conv_reg[i](feat)
+            # cls prediction
+            cls_score = F.sigmoid(cls_logit)
+            cls_score_list.append(cls_score.flatten(2).transpose([0, 2, 1]))
+            # reg prediction
+            reg_xywh, obj_logit = paddle.split(reg_pred, [4, 1], axis=1)
+            reg_xywh = reg_xywh.flatten(2).transpose([0, 2, 1])
+            reg_pred_list.append(reg_xywh)
+            # obj prediction
+            obj_score = F.sigmoid(obj_logit)
+            obj_score_list.append(obj_score.flatten(2).transpose([0, 2, 1]))
+
+        cls_score_list = paddle.concat(cls_score_list, axis=1)
+        reg_pred_list = paddle.concat(reg_pred_list, axis=1)
+        obj_score_list = paddle.concat(obj_score_list, axis=1)
+
+        # bbox decode
+        anchor_points, stride_tensor, _ =\
+            self._generate_anchor_point(feat_sizes, self.fpn_strides)
+        reg_xy, reg_wh = paddle.split(reg_pred_list, 2, axis=-1)
+        reg_xy += (anchor_points / stride_tensor)
+        reg_wh = paddle.exp(reg_wh) * 0.5
+        bbox_pred_list = paddle.concat(
+            [reg_xy - reg_wh, reg_xy + reg_wh], axis=-1)
+
+        if self.training:
+            anchor_points, stride_tensor, num_anchors_list =\
+                self._generate_anchor_point(feat_sizes, self.fpn_strides, 0.5)
+            yolox_losses = self.get_loss([
+                cls_score_list, bbox_pred_list, obj_score_list, anchor_points,
+                stride_tensor, num_anchors_list
+            ], targets)
+            return yolox_losses
+        else:
+            pred_scores = (cls_score_list * obj_score_list).sqrt()
+            return pred_scores, bbox_pred_list, stride_tensor
+
+    def get_loss(self, head_outs, targets):
+        pred_cls, pred_bboxes, pred_obj,\
+        anchor_points, stride_tensor, num_anchors_list = head_outs
+        gt_labels = targets['gt_class']
+        gt_bboxes = targets['gt_bbox']
+        pred_scores = (pred_cls * pred_obj).sqrt()
+        # label assignment
+        center_and_strides = paddle.concat(
+            [anchor_points, stride_tensor, stride_tensor], axis=-1)
+        pos_num_list, label_list, bbox_target_list = [], [], []
+        for pred_score, pred_bbox, gt_box, gt_label in zip(
+                pred_scores.detach(),
+                pred_bboxes.detach() * stride_tensor, gt_bboxes, gt_labels):
+            pos_num, label, _, bbox_target = self.assigner(
+                pred_score, center_and_strides, pred_bbox, gt_box, gt_label)
+            pos_num_list.append(pos_num)
+            label_list.append(label)
+            bbox_target_list.append(bbox_target)
+        labels = paddle.to_tensor(np.stack(label_list, axis=0))
+        bbox_targets = paddle.to_tensor(np.stack(bbox_target_list, axis=0))
+        bbox_targets /= stride_tensor  # rescale bbox
+
+        # 1. obj score loss
+        mask_positive = (labels != self.num_classes)
+        loss_obj = F.binary_cross_entropy(
+            pred_obj,
+            mask_positive.astype(pred_obj.dtype).unsqueeze(-1),
+            reduction='sum')
+
+        num_pos = sum(pos_num_list)
+
+        if num_pos > 0:
+            num_pos = paddle.to_tensor(num_pos, dtype=self._dtype).clip(min=1)
+            loss_obj /= num_pos
+
+            # 2. iou loss
+            bbox_mask = mask_positive.unsqueeze(-1).tile([1, 1, 4])
+            pred_bboxes_pos = paddle.masked_select(pred_bboxes,
+                                                   bbox_mask).reshape([-1, 4])
+            assigned_bboxes_pos = paddle.masked_select(
+                bbox_targets, bbox_mask).reshape([-1, 4])
+            bbox_iou = bbox_overlaps(pred_bboxes_pos, assigned_bboxes_pos)
+            bbox_iou = paddle.diag(bbox_iou)
+
+            loss_iou = self.iou_loss(
+                pred_bboxes_pos.split(
+                    4, axis=-1),
+                assigned_bboxes_pos.split(
+                    4, axis=-1))
+            loss_iou = loss_iou.sum() / num_pos
+
+            # 3. cls loss
+            cls_mask = mask_positive.unsqueeze(-1).tile(
+                [1, 1, self.num_classes])
+            pred_cls_pos = paddle.masked_select(
+                pred_cls, cls_mask).reshape([-1, self.num_classes])
+            assigned_cls_pos = paddle.masked_select(labels, mask_positive)
+            assigned_cls_pos = F.one_hot(assigned_cls_pos,
+                                         self.num_classes + 1)[..., :-1]
+            assigned_cls_pos *= bbox_iou.unsqueeze(-1)
+            loss_cls = F.binary_cross_entropy(
+                pred_cls_pos, assigned_cls_pos, reduction='sum')
+            loss_cls /= num_pos
+
+            # 4. l1 loss
+            if targets['epoch_id'] >= self.l1_epoch:
+                loss_l1 = F.l1_loss(
+                    pred_bboxes_pos, assigned_bboxes_pos, reduction='sum')
+                loss_l1 /= num_pos
+            else:
+                loss_l1 = paddle.zeros([1])
+                loss_l1.stop_gradient = False
+        else:
+            loss_cls = paddle.zeros([1])
+            loss_iou = paddle.zeros([1])
+            loss_l1 = paddle.zeros([1])
+            loss_cls.stop_gradient = False
+            loss_iou.stop_gradient = False
+            loss_l1.stop_gradient = False
+
+        loss = self.loss_weight['obj'] * loss_obj + \
+               self.loss_weight['cls'] * loss_cls + \
+               self.loss_weight['iou'] * loss_iou
+
+        if targets['epoch_id'] >= self.l1_epoch:
+            loss += (self.loss_weight['l1'] * loss_l1)
+
+        yolox_losses = {
+            'loss': loss,
+            'loss_cls': loss_cls,
+            'loss_obj': loss_obj,
+            'loss_iou': loss_iou,
+            'loss_l1': loss_l1,
+        }
+        return yolox_losses
+
+    def post_process(self, head_outs, img_shape, scale_factor):
+        pred_scores, pred_bboxes, stride_tensor = head_outs
+        pred_scores = pred_scores.transpose([0, 2, 1])
+        pred_bboxes *= stride_tensor
+        # scale bbox to origin image
+        scale_factor = scale_factor.flip(-1).tile([1, 2]).unsqueeze(1)
+        pred_bboxes /= scale_factor
+        bbox_pred, bbox_num, _ = self.nms(pred_bboxes, pred_scores)
+        return bbox_pred, bbox_num
diff --git a/ppdet/modeling/initializer.py b/ppdet/modeling/initializer.py
index b7a135dcca7309be09fa4819e21d77a02d332d57..b482f133dd9ac1e2568f5c971f004117c56a5368 100644
--- a/ppdet/modeling/initializer.py
+++ b/ppdet/modeling/initializer.py
@@ -273,7 +273,8 @@ def linear_init_(module):
 def conv_init_(module):
     bound = 1 / np.sqrt(np.prod(module.weight.shape[1:]))
     uniform_(module.weight, -bound, bound)
-    uniform_(module.bias, -bound, bound)
+    if module.bias is not None:
+        uniform_(module.bias, -bound, bound)
 
 
 def bias_init_with_prob(prior_prob=0.01):
diff --git a/ppdet/modeling/necks/yolo_fpn.py b/ppdet/modeling/necks/yolo_fpn.py
index bc06b14dba4fb5a2e5570162a6151927cb2df8da..1aaf593f0611d2af9e23c4bfd4c4c2cc326b5ba2 100644
--- a/ppdet/modeling/necks/yolo_fpn.py
+++ b/ppdet/modeling/necks/yolo_fpn.py
@@ -1,15 +1,15 @@
-# Copyright (c) 2020 PaddlePaddle Authors. All Rights Reserved.
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
+# Copyright (c) 2020 PaddlePaddle Authors. All Rights Reserved. 
+#   
+# Licensed under the Apache License, Version 2.0 (the "License");   
+# you may not use this file except in compliance with the License.  
+# You may obtain a copy of the License at   
+#   
+#     http://www.apache.org/licenses/LICENSE-2.0    
+# 
+# Unless required by applicable law or agreed to in writing, software   
+# distributed under the License is distributed on an "AS IS" BASIS, 
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  
+# See the License for the specific language governing permissions and   
 # limitations under the License.
 
 import paddle
@@ -19,8 +19,9 @@ from ppdet.core.workspace import register, serializable
 from ppdet.modeling.layers import DropBlock
 from ..backbones.darknet import ConvBNLayer
 from ..shape_spec import ShapeSpec
+from ..backbones.csp_darknet import BaseConv, DWConv, CSPLayer
 
-__all__ = ['YOLOv3FPN', 'PPYOLOFPN', 'PPYOLOTinyFPN', 'PPYOLOPAN']
+__all__ = ['YOLOv3FPN', 'PPYOLOFPN', 'PPYOLOTinyFPN', 'PPYOLOPAN', 'YOLOCSPPAN']
 
 
 def add_coord(x, data_format):
@@ -986,3 +987,102 @@ class PPYOLOPAN(nn.Layer):
     @property
     def out_shape(self):
         return [ShapeSpec(channels=c) for c in self._out_channels]
+
+
+@register
+@serializable
+class YOLOCSPPAN(nn.Layer):
+    """
+    YOLO CSP-PAN, used in YOLOv5 and YOLOX.
+    """
+    __shared__ = ['depth_mult', 'act']
+
+    def __init__(self,
+                 depth_mult=1.0,
+                 in_channels=[256, 512, 1024],
+                 depthwise=False,
+                 act='silu'):
+        super(YOLOCSPPAN, self).__init__()
+        self.in_channels = in_channels
+        self._out_channels = in_channels
+        Conv = DWConv if depthwise else BaseConv
+
+        self.upsample = nn.Upsample(scale_factor=2, mode="nearest")
+
+        # top-down fpn
+        self.lateral_convs = nn.LayerList()
+        self.fpn_blocks = nn.LayerList()
+        for idx in range(len(in_channels) - 1, 0, -1):
+            self.lateral_convs.append(
+                BaseConv(
+                    int(in_channels[idx]),
+                    int(in_channels[idx - 1]),
+                    1,
+                    1,
+                    act=act))
+            self.fpn_blocks.append(
+                CSPLayer(
+                    int(in_channels[idx - 1] * 2),
+                    int(in_channels[idx - 1]),
+                    round(3 * depth_mult),
+                    shortcut=False,
+                    depthwise=depthwise,
+                    act=act))
+
+        # bottom-up pan
+        self.downsample_convs = nn.LayerList()
+        self.pan_blocks = nn.LayerList()
+        for idx in range(len(in_channels) - 1):
+            self.downsample_convs.append(
+                Conv(
+                    int(in_channels[idx]),
+                    int(in_channels[idx]),
+                    3,
+                    stride=2,
+                    act=act))
+            self.pan_blocks.append(
+                CSPLayer(
+                    int(in_channels[idx] * 2),
+                    int(in_channels[idx + 1]),
+                    round(3 * depth_mult),
+                    shortcut=False,
+                    depthwise=depthwise,
+                    act=act))
+
+    def forward(self, feats, for_mot=False):
+        assert len(feats) == len(self.in_channels)
+
+        # top-down fpn
+        inner_outs = [feats[-1]]
+        for idx in range(len(self.in_channels) - 1, 0, -1):
+            feat_heigh = inner_outs[0]
+            feat_low = feats[idx - 1]
+            feat_heigh = self.lateral_convs[len(self.in_channels) - 1 - idx](
+                feat_heigh)
+            inner_outs[0] = feat_heigh
+
+            upsample_feat = self.upsample(feat_heigh)
+            inner_out = self.fpn_blocks[len(self.in_channels) - 1 - idx](
+                paddle.concat(
+                    [upsample_feat, feat_low], axis=1))
+            inner_outs.insert(0, inner_out)
+
+        # bottom-up pan
+        outs = [inner_outs[0]]
+        for idx in range(len(self.in_channels) - 1):
+            feat_low = outs[-1]
+            feat_height = inner_outs[idx + 1]
+            downsample_feat = self.downsample_convs[idx](feat_low)
+            out = self.pan_blocks[idx](paddle.concat(
+                [downsample_feat, feat_height], axis=1))
+            outs.append(out)
+
+        return outs
+
+    @classmethod
+    def from_config(cls, cfg, input_shape):
+        return {'in_channels': [i.channels for i in input_shape], }
+
+    @property
+    def out_shape(self):
+        return [ShapeSpec(channels=c) for c in self._out_channels]
diff --git a/ppdet/modeling/ops.py b/ppdet/modeling/ops.py
index 67e8960ca115c1c6b5338fa7c84a26c1d4873fbf..ab7724301f4f7fe6126bd9a95a3728f232363769 100644
--- a/ppdet/modeling/ops.py
+++ b/ppdet/modeling/ops.py
@@ -1,15 +1,15 @@
-#   Copyright (c) 2020 PaddlePaddle Authors. All Rights Reserved.
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
+# Copyright (c) 2020 PaddlePaddle Authors. All Rights Reserved. 
+#   
+# Licensed under the Apache License, Version 2.0 (the "License");   
+# you may not use this file except in compliance with the License.  
+# You may obtain a copy of the License at   
+#   
+#     http://www.apache.org/licenses/LICENSE-2.0    
+# 
+# Unless required by applicable law or agreed to in writing, software   
+# distributed under the License is distributed on an "AS IS" BASIS, 
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  
+# See the License for the specific language governing permissions and   
 # limitations under the License.
 
 import paddle
@@ -29,7 +29,7 @@ __all__ = [
     'roi_pool', 'roi_align', 'prior_box', 'generate_proposals',
     'iou_similarity', 'box_coder', 'yolo_box', 'multiclass_nms',
     'distribute_fpn_proposals', 'collect_fpn_proposals', 'matrix_nms',
-    'batch_norm', 'mish', 'swish', 'identity'
+    'batch_norm', 'get_activation', 'mish', 'swish', 'identity'
 ]
 
 
@@ -107,6 +107,18 @@ def batch_norm(ch,
     return norm_layer
 
 
+def get_activation(name="silu"):
+    if name == "silu":
+        module = nn.Silu()
+    elif name == "relu":
+        module = nn.ReLU()
+    elif name == "leakyrelu":
+        module = nn.LeakyReLU(0.1)
+    else:
+        raise AttributeError("Unsupported act type: {}".format(name))
+    return module
+
+
 @paddle.jit.not_to_static
 def roi_pool(input,
              rois,
@@ -1012,7 +1024,7 @@ def multiclass_nms(bboxes,
                  nms_threshold, 'keep_top_k', keep_top_k, 'nms_eta', nms_eta,
                  'normalized', normalized)
         output, index, nms_rois_num = _C_ops.multiclass_nms3(bboxes, scores,
-                                                               rois_num, *attrs)
+                                                             rois_num, *attrs)
         if not return_index:
             index = None
         return output, nms_rois_num, index
diff --git a/ppdet/optimizer.py b/ppdet/optimizer.py
index 1305b76fed48c6acd3967928ffc82b74ef5a881d..98a5e5f9caa4bbf436009b9f3860222648bf716b 100644
--- a/ppdet/optimizer.py
+++ b/ppdet/optimizer.py
@@ -209,6 +209,33 @@ class BurninWarmup(object):
         return boundary, value
 
 
+@serializable
+class ExpWarmup(object):
+    """
+    Warm up learning rate in exponential mode
+    Args:
+        steps (int): warm up steps.
+        epochs (int|None): use epochs as warm up steps, the priority
+            of `epochs` is higher than `steps`. Default: None.
+    """
+
+    def __init__(self, steps=5, epochs=None):
+        super(ExpWarmup, self).__init__()
+        self.steps = steps
+        self.epochs = epochs
+
+    def __call__(self, base_lr, step_per_epoch):
+        boundary = []
+        value = []
+        warmup_steps = self.epochs * step_per_epoch if self.epochs is not None else self.steps
+        for i in range(warmup_steps + 1):
+            factor = (i / float(warmup_steps))**2
+            value.append(base_lr * factor)
+            if i > 0:
+                boundary.append(i)
+        return boundary, value
+
+
 @register
 class LearningRate(object):
     """
@@ -331,7 +358,8 @@ class ModelEMA(object):
             Ema's parameter are updated with the formula:
            `ema_param = decay * ema_param + (1 - decay) * cur_param`.
             Defaults is 0.9998.
-        use_thres_step (bool): Whether set decay by thres_step or not
+        ema_decay_type (str): type in ['threshold', 'normal', 'exponential'],
+            'threshold' as default.
         cycle_epoch (int): The epoch of interval to reset ema_param and
             step. Defaults is -1, which means not reset. Its function is to
             add a regular effect to ema, which is set according to experience
@@ -341,7 +369,7 @@ class ModelEMA(object):
     def __init__(self,
                  model,
                  decay=0.9998,
-                 use_thres_step=False,
+                 ema_decay_type='threshold',
                  cycle_epoch=-1):
         self.step = 0
         self.epoch = 0
@@ -349,7 +377,7 @@ class ModelEMA(object):
         self.state_dict = dict()
         for k, v in model.state_dict().items():
             self.state_dict[k] = paddle.zeros_like(v)
-        self.use_thres_step = use_thres_step
+        self.ema_decay_type = ema_decay_type
         self.cycle_epoch = cycle_epoch
 
         self._model_state = {
@@ -370,8 +398,10 @@ class ModelEMA(object):
         self.step = step
 
     def update(self, model=None):
-        if self.use_thres_step:
+        if self.ema_decay_type == 'threshold':
             decay = min(self.decay, (1 + self.step) / (10 + self.step))
+        elif self.ema_decay_type == 'exponential':
+            decay = self.decay * (1 - math.exp(-(self.step + 1) / 2000))
         else:
             decay = self.decay
         self._decay = decay
@@ -394,7 +424,8 @@ class ModelEMA(object):
             return self.state_dict
         state_dict = dict()
         for k, v in self.state_dict.items():
-            v = v / (1 - self._decay**self.step)
+            if self.ema_decay_type != 'exponential':
+                v = v / (1 - self._decay**self.step)
             v.stop_gradient = True
             state_dict[k] = v
         self.epoch += 1