diff --git a/deploy/python/keypoint_preprocess.py b/deploy/python/keypoint_preprocess.py
index 97a747c4ca0522d691dad5998e81088647f57ae1..07e097b9b4ff552eba25c72319913dd6c8920505 100644
--- a/deploy/python/keypoint_preprocess.py
+++ b/deploy/python/keypoint_preprocess.py
@@ -109,7 +109,10 @@ def get_affine_transform(center,
 
 
 def get_warp_matrix(theta, size_input, size_dst, size_target):
-    """Calculate the transformation matrix under the constraint of unbiased.
+    """This code is based on 
+        https://github.com/open-mmlab/mmpose/blob/master/mmpose/core/post_processing/post_transforms.py
+
+        Calculate the transformation matrix under the constraint of unbiased.
     Paper ref: Huang et al. The Devil is in the Details: Delving into Unbiased
     Data Processing for Human Pose Estimation (CVPR 2020).
 
diff --git a/ppdet/data/transform/keypoint_operators.py b/ppdet/data/transform/keypoint_operators.py
index 81770b63efd76e62435af52b4ab1f5318ebcf988..48957faaa236e612cd10e4ebd704c857777a006d 100644
--- a/ppdet/data/transform/keypoint_operators.py
+++ b/ppdet/data/transform/keypoint_operators.py
@@ -790,7 +790,10 @@ class ToHeatmapsTopDown_DARK(object):
 
 @register_keypointop
 class ToHeatmapsTopDown_UDP(object):
-    """to generate the gaussian heatmaps of keypoint for heatmap loss.
+    """This code is based on:
+        https://github.com/HuangJunJie2017/UDP-Pose/blob/master/deep-high-resolution-net.pytorch/lib/dataset/JointsDataset.py
+       
+        to generate the gaussian heatmaps of keypoint for heatmap loss.
         ref: Huang et al. The Devil is in the Details: Delving into Unbiased Data Processing
         for Human Pose Estimation (CVPR 2020).
 
diff --git a/ppdet/modeling/backbones/lite_hrnet.py b/ppdet/modeling/backbones/lite_hrnet.py
index da98be3a4b3323bc9f4b77ff31202009f43b2b1a..8f0ded109442a890f6f0b92155d5ee18e3d5b799 100644
--- a/ppdet/modeling/backbones/lite_hrnet.py
+++ b/ppdet/modeling/backbones/lite_hrnet.py
@@ -11,6 +11,10 @@
 # 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.
+"""
+This code is based on
+https://github.com/HRNet/Lite-HRNet/blob/hrnet/models/backbones/litehrnet.py
+"""
 
 import paddle
 import paddle.nn as nn
diff --git a/ppdet/modeling/keypoint_utils.py b/ppdet/modeling/keypoint_utils.py
index b3f84da7dcff694a6c91b67db3f534559412d458..4910eb0b7277f614e38b501f4540cd67dd33fc94 100644
--- a/ppdet/modeling/keypoint_utils.py
+++ b/ppdet/modeling/keypoint_utils.py
@@ -96,7 +96,10 @@ def get_affine_transform(center,
 
 
 def get_warp_matrix(theta, size_input, size_dst, size_target):
-    """Calculate the transformation matrix under the constraint of unbiased.
+    """This code is based on
+        https://github.com/open-mmlab/mmpose/blob/master/mmpose/core/post_processing/post_transforms.py
+
+        Calculate the transformation matrix under the constraint of unbiased.
     Paper ref: Huang et al. The Devil is in the Details: Delving into Unbiased
     Data Processing for Human Pose Estimation (CVPR 2020).