diff --git a/examples/DQN/README.md b/examples/DQN/README.md
new file mode 100644
index 0000000000000000000000000000000000000000..570ae9619ed754fbf146dfdf86248681a7ee5d46
--- /dev/null
+++ b/examples/DQN/README.md
@@ -0,0 +1,27 @@
+## Reproduce DQN with PARL
+Based on PARL, the DQN model of deep reinforcement learning is reproduced, and the same level of indicators of the paper is reproduced in the classic Atari game.
+
++ DQN in
+[Human-level Control Through Deep Reinforcement Learning](http://www.nature.com/nature/journal/v518/n7540/full/nature14236.html)
+
+### Atari games introduction
+Please see [here](https://gym.openai.com/envs/#atari) to know more about Atari game.
+
+
+## How to use
+### Dependencies:
++ python2.7 or python3.5+
++ [PARL](https://github.com/PaddlePaddle/PARL)
++ [paddlepaddle>=1.0.0](https://github.com/PaddlePaddle/Paddle)
++ gym
++ tqdm
++ opencv-python
++ ale_python_interface
+
+
+### Start Training:
+```
+# To train a model for Pong game with CUDA
+python train.py --rom ./rom_files/pong.bin --use_cuda
+```
+> To train more games, you can install more rom files from [here](https://github.com/openai/atari-py/tree/master/atari_py/atari_roms).
diff --git a/examples/DQN/atari.py b/examples/DQN/atari.py
new file mode 100644
index 0000000000000000000000000000000000000000..35a6801e9a04af919ad20756b353711caa99ad33
--- /dev/null
+++ b/examples/DQN/atari.py
@@ -0,0 +1,168 @@
+#   Copyright (c) 2018 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 cv2
+import gym
+import numpy as np
+import os
+import threading
+from atari_py import ALEInterface
+from gym import spaces
+from gym.envs.atari.atari_env import ACTION_MEANING
+
+__all__ = ['AtariPlayer']
+
+ROM_URL = "https://github.com/openai/atari-py/tree/master/atari_py/atari_roms"
+_ALE_LOCK = threading.Lock()
+"""
+The following AtariPlayer are copied or modified from tensorpack/tensorpack:
+    https://github.com/tensorpack/tensorpack/blob/master/examples/DeepQNetwork/atari.py
+"""
+
+
+class AtariPlayer(gym.Env):
+    """
+    A wrapper for ALE emulator, with configurations to mimic DeepMind DQN settings.
+    Info:
+        score: the accumulated reward in the current game
+        gameOver: True when the current game is Over
+    """
+
+    def __init__(self,
+                 rom_file,
+                 viz=0,
+                 frame_skip=4,
+                 nullop_start=30,
+                 live_lost_as_eoe=True,
+                 max_num_frames=0):
+        """
+        Args:
+            rom_file: path to the rom
+            frame_skip: skip every k frames and repeat the action
+            viz: visualization to be done.
+                Set to 0 to disable.
+                Set to a positive number to be the delay between frames to show.
+                Set to a string to be a directory to store frames.
+            nullop_start: start with random number of null ops.
+            live_losts_as_eoe: consider lost of lives as end of episode. Useful for training.
+            max_num_frames: maximum number of frames per episode.
+        """
+        super(AtariPlayer, self).__init__()
+        assert os.path.isfile(rom_file), \
+            "rom {} not found. Please download at {}".format(rom_file, ROM_URL)
+
+        try:
+            ALEInterface.setLoggerMode(ALEInterface.Logger.Error)
+        except AttributeError:
+            print("You're not using latest ALE")
+
+        # avoid simulator bugs: https://github.com/mgbellemare/Arcade-Learning-Environment/issues/86
+        with _ALE_LOCK:
+            self.ale = ALEInterface()
+            self.ale.setInt(b"random_seed", np.random.randint(0, 30000))
+            self.ale.setInt(b"max_num_frames_per_episode", max_num_frames)
+            self.ale.setBool(b"showinfo", False)
+
+            self.ale.setInt(b"frame_skip", 1)
+            self.ale.setBool(b'color_averaging', False)
+            # manual.pdf suggests otherwise.
+            self.ale.setFloat(b'repeat_action_probability', 0.0)
+
+            # viz setup
+            if isinstance(viz, str):
+                assert os.path.isdir(viz), viz
+                self.ale.setString(b'record_screen_dir', viz)
+                viz = 0
+            if isinstance(viz, int):
+                viz = float(viz)
+            self.viz = viz
+            if self.viz and isinstance(self.viz, float):
+                self.windowname = os.path.basename(rom_file)
+                cv2.startWindowThread()
+                cv2.namedWindow(self.windowname)
+
+            self.ale.loadROM(rom_file.encode('utf-8'))
+        self.width, self.height = self.ale.getScreenDims()
+        self.actions = self.ale.getMinimalActionSet()
+
+        self.live_lost_as_eoe = live_lost_as_eoe
+        self.frame_skip = frame_skip
+        self.nullop_start = nullop_start
+
+        self.action_space = spaces.Discrete(len(self.actions))
+        self.observation_space = spaces.Box(
+            low=0, high=255, shape=(self.height, self.width), dtype=np.uint8)
+        self._restart_episode()
+
+    def get_action_meanings(self):
+        return [ACTION_MEANING[i] for i in self.actions]
+
+    def _grab_raw_image(self):
+        """
+        :returns: the current 3-channel image
+        """
+        m = self.ale.getScreenRGB()
+        return m.reshape((self.height, self.width, 3))
+
+    def _current_state(self):
+        """
+        returns: a gray-scale (h, w) uint8 image
+        """
+        ret = self._grab_raw_image()
+        # avoid missing frame issue: max-pooled over the last screen
+        ret = np.maximum(ret, self.last_raw_screen)
+        if self.viz:
+            if isinstance(self.viz, float):
+                cv2.imshow(self.windowname, ret)
+                cv2.waitKey(int(self.viz * 1000))
+        ret = ret.astype('float32')
+        # 0.299,0.587.0.114. same as rgb2y in torch/image
+        ret = cv2.cvtColor(ret, cv2.COLOR_RGB2GRAY)
+        return ret.astype('uint8')  # to save some memory
+
+    def _restart_episode(self):
+        with _ALE_LOCK:
+            self.ale.reset_game()
+
+        # random null-ops start
+        n = np.random.randint(self.nullop_start)
+        self.last_raw_screen = self._grab_raw_image()
+        for k in range(n):
+            if k == n - 1:
+                self.last_raw_screen = self._grab_raw_image()
+            self.ale.act(0)
+
+    def reset(self):
+        if self.ale.game_over():
+            self._restart_episode()
+        return self._current_state()
+
+    def step(self, act):
+        oldlives = self.ale.lives()
+        r = 0
+        for k in range(self.frame_skip):
+            if k == self.frame_skip - 1:
+                self.last_raw_screen = self._grab_raw_image()
+            r += self.ale.act(self.actions[act])
+            newlives = self.ale.lives()
+            if self.ale.game_over() or \
+                    (self.live_lost_as_eoe and newlives < oldlives):
+                break
+
+        isOver = self.ale.game_over()
+        if self.live_lost_as_eoe:
+            isOver = isOver or newlives < oldlives
+
+        info = {'ale.lives': newlives}
+        return self._current_state(), r, isOver, info
diff --git a/examples/DQN/atari_agent.py b/examples/DQN/atari_agent.py
new file mode 100644
index 0000000000000000000000000000000000000000..bcdf3c0e4c42c11b80b00f006a041c1708364805
--- /dev/null
+++ b/examples/DQN/atari_agent.py
@@ -0,0 +1,103 @@
+#   Copyright (c) 2018 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 numpy as np
+import paddle.fluid as fluid
+import parl.layers as layers
+from parl.framework.agent_base import Agent
+from parl.utils import logger
+
+IMAGE_SIZE = (84, 84)
+CONTEXT_LEN = 4
+
+
+class AtariAgent(Agent):
+    def __init__(self, algorithm, action_dim):
+        super(AtariAgent, self).__init__(algorithm)
+
+        self.exploration = 1.1
+        self.action_dim = action_dim
+        self.global_step = 0
+        self.update_target_steps = 10000 // 4
+
+    def build_program(self):
+        self.pred_program = fluid.Program()
+        self.train_program = fluid.Program()
+        with fluid.program_guard(self.pred_program):
+            obs = layers.data(
+                name='obs',
+                shape=[CONTEXT_LEN, IMAGE_SIZE[0], IMAGE_SIZE[1]],
+                dtype='float32')
+            self.value = self.alg.define_predict(obs)
+
+        with fluid.program_guard(self.train_program):
+            obs = layers.data(
+                name='obs',
+                shape=[CONTEXT_LEN, IMAGE_SIZE[0], IMAGE_SIZE[1]],
+                dtype='float32')
+            action = layers.data(name='act', shape=[1], dtype='int32')
+            reward = layers.data(name='reward', shape=[], dtype='float32')
+            next_obs = layers.data(
+                name='next_obs',
+                shape=[CONTEXT_LEN, IMAGE_SIZE[0], IMAGE_SIZE[1]],
+                dtype='float32')
+            terminal = layers.data(name='terminal', shape=[], dtype='bool')
+            self.cost = self.alg.define_learn(obs, action, reward, next_obs,
+                                              terminal)
+
+    def sample(self, obs):
+        sample = np.random.random()
+        if sample < self.exploration:
+            act = np.random.randint(self.action_dim)
+        else:
+            if np.random.random() < 0.01:
+                act = np.random.randint(self.action_dim)
+            else:
+                obs = np.expand_dims(obs, axis=0)
+                pred_Q = self.fluid_executor.run(
+                    self.pred_program,
+                    feed={'obs': obs.astype('float32')},
+                    fetch_list=[self.value])[0]
+                pred_Q = np.squeeze(pred_Q, axis=0)
+                act = np.argmax(pred_Q)
+        self.exploration = max(0.1, self.exploration - 1e-6)
+        return act
+
+    def predict(self, obs):
+        obs = np.expand_dims(obs, axis=0)
+        pred_Q = self.fluid_executor.run(
+            self.pred_program,
+            feed={'obs': obs.astype('float32')},
+            fetch_list=[self.value])[0]
+        pred_Q = np.squeeze(pred_Q, axis=0)
+        act = np.argmax(pred_Q)
+        return act
+
+    def learn(self, obs, act, reward, next_obs, terminal):
+        if self.global_step % self.update_target_steps == 0:
+            self.alg.sync_target(self.gpu_id)
+        self.global_step += 1
+
+        act = np.expand_dims(act, -1)
+        reward = np.clip(reward, -1, 1)
+        feed = {
+            'obs': obs.astype('float32'),
+            'act': act.astype('int32'),
+            'reward': reward,
+            'next_obs': next_obs.astype('float32'),
+            'terminal': terminal
+        }
+        cost = self.fluid_executor.run(
+            self.train_program, feed=feed, fetch_list=[self.cost])[0]
+        return cost
diff --git a/examples/DQN/atari_model.py b/examples/DQN/atari_model.py
new file mode 100644
index 0000000000000000000000000000000000000000..0ea1de97a251dbd4651c794bfe3b6a2bf6b2ae6f
--- /dev/null
+++ b/examples/DQN/atari_model.py
@@ -0,0 +1,51 @@
+#   Copyright (c) 2018 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.fluid as fluid
+import parl.layers as layers
+from parl.framework.model_base import Model
+from parl.utils import logger
+
+
+class AtariModel(Model):
+    def __init__(self, img_height, img_width, act_dim):
+        self.img_height = img_height
+        self.img_width = img_width
+        self.act_dim = act_dim
+
+        self.conv1 = layers.conv2d(
+            num_filters=32, filter_size=5, stride=1, padding=2, act='relu')
+        self.conv2 = layers.conv2d(
+            num_filters=32, filter_size=5, stride=1, padding=2, act='relu')
+        self.conv3 = layers.conv2d(
+            num_filters=64, filter_size=4, stride=1, padding=1, act='relu')
+        self.conv4 = layers.conv2d(
+            num_filters=64, filter_size=3, stride=1, padding=1, act='relu')
+        self.fc1 = layers.fc(size=act_dim)
+
+    def value(self, obs):
+        obs = obs / 255.0
+        out = self.conv1(obs)
+        out = layers.pool2d(
+            input=out, pool_size=2, pool_stride=2, pool_type='max')
+        out = self.conv2(out)
+        out = layers.pool2d(
+            input=out, pool_size=2, pool_stride=2, pool_type='max')
+        out = self.conv3(out)
+        out = layers.pool2d(
+            input=out, pool_size=2, pool_stride=2, pool_type='max')
+        out = self.conv4(out)
+        out = layers.flatten(out, axis=1)
+        out = self.fc1(out)
+        return out
diff --git a/examples/DQN/atari_wrapper.py b/examples/DQN/atari_wrapper.py
new file mode 100644
index 0000000000000000000000000000000000000000..4195075faab5eb480942a8afdbd393183fac1fca
--- /dev/null
+++ b/examples/DQN/atari_wrapper.py
@@ -0,0 +1,115 @@
+#   Copyright (c) 2018 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 gym
+import numpy as np
+from collections import deque
+from gym import spaces
+
+_v0, _v1 = gym.__version__.split('.')[:2]
+assert int(_v0) > 0 or int(_v1) >= 10, gym.__version__
+"""
+The following wrappers are copied or modified from openai/baselines:
+https://github.com/openai/baselines/blob/master/baselines/common/atari_wrappers.py
+"""
+
+
+class MapState(gym.ObservationWrapper):
+    def __init__(self, env, map_func):
+        gym.ObservationWrapper.__init__(self, env)
+        self._func = map_func
+
+    def observation(self, obs):
+        return self._func(obs)
+
+
+class FrameStack(gym.Wrapper):
+    def __init__(self, env, k):
+        """Buffer observations and stack across channels (last axis)."""
+        gym.Wrapper.__init__(self, env)
+        self.k = k
+        self.frames = deque([], maxlen=k)
+        shp = env.observation_space.shape
+        chan = 1 if len(shp) == 2 else shp[2]
+        self.observation_space = spaces.Box(
+            low=0, high=255, shape=(shp[0], shp[1], chan * k), dtype=np.uint8)
+
+    def reset(self):
+        """Clear buffer and re-fill by duplicating the first observation."""
+        ob = self.env.reset()
+        for _ in range(self.k - 1):
+            self.frames.append(np.zeros_like(ob))
+        self.frames.append(ob)
+        return self.observation()
+
+    def step(self, action):
+        ob, reward, done, info = self.env.step(action)
+        self.frames.append(ob)
+        return self.observation(), reward, done, info
+
+    def observation(self):
+        assert len(self.frames) == self.k
+        return np.stack(self.frames, axis=0)
+
+
+class _FireResetEnv(gym.Wrapper):
+    def __init__(self, env):
+        """Take action on reset for environments that are fixed until firing."""
+        gym.Wrapper.__init__(self, env)
+        assert env.unwrapped.get_action_meanings()[1] == 'FIRE'
+        assert len(env.unwrapped.get_action_meanings()) >= 3
+
+    def reset(self):
+        self.env.reset()
+        obs, _, done, _ = self.env.step(1)
+        if done:
+            self.env.reset()
+        obs, _, done, _ = self.env.step(2)
+        if done:
+            self.env.reset()
+        return obs
+
+    def step(self, action):
+        return self.env.step(action)
+
+
+def FireResetEnv(env):
+    if isinstance(env, gym.Wrapper):
+        baseenv = env.unwrapped
+    else:
+        baseenv = env
+    if 'FIRE' in baseenv.get_action_meanings():
+        return _FireResetEnv(env)
+    return env
+
+
+class LimitLength(gym.Wrapper):
+    def __init__(self, env, k):
+        gym.Wrapper.__init__(self, env)
+        self.k = k
+
+    def reset(self):
+        # This assumes that reset() will really reset the env.
+        # If the underlying env tries to be smart about reset
+        # (e.g. end-of-life), the assumption doesn't hold.
+        ob = self.env.reset()
+        self.cnt = 0
+        return ob
+
+    def step(self, action):
+        ob, r, done, info = self.env.step(action)
+        self.cnt += 1
+        if self.cnt == self.k:
+            done = True
+        return ob, r, done, info
diff --git a/examples/DQN/expreplay.py b/examples/DQN/expreplay.py
new file mode 100644
index 0000000000000000000000000000000000000000..6e7e2ba25bed33ab538ca6d7d383f588af651975
--- /dev/null
+++ b/examples/DQN/expreplay.py
@@ -0,0 +1,111 @@
+#   Copyright (c) 2018 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 numpy as np
+import copy
+from collections import deque, namedtuple
+
+Experience = namedtuple('Experience', ['state', 'action', 'reward', 'isOver'])
+
+
+class ReplayMemory(object):
+    def __init__(self, max_size, state_shape, context_len):
+        self.max_size = int(max_size)
+        self.state_shape = state_shape
+        self.context_len = int(context_len)
+
+        self.state = np.zeros((self.max_size, ) + state_shape, dtype='uint8')
+        self.action = np.zeros((self.max_size, ), dtype='int32')
+        self.reward = np.zeros((self.max_size, ), dtype='float32')
+        self.isOver = np.zeros((self.max_size, ), dtype='bool')
+
+        self._curr_size = 0
+        self._curr_pos = 0
+        self._context = deque(maxlen=context_len - 1)
+
+    def append(self, exp):
+        """append a new experience into replay memory
+        """
+        if self._curr_size < self.max_size:
+            self._assign(self._curr_pos, exp)
+            self._curr_size += 1
+        else:
+            self._assign(self._curr_pos, exp)
+        self._curr_pos = (self._curr_pos + 1) % self.max_size
+        if exp.isOver:
+            self._context.clear()
+        else:
+            self._context.append(exp)
+
+    def recent_state(self):
+        """ maintain recent state for training"""
+        lst = list(self._context)
+        states = [np.zeros(self.state_shape, dtype='uint8')] * \
+                    (self._context.maxlen - len(lst))
+        states.extend([k.state for k in lst])
+        return states
+
+    def sample(self, idx):
+        """ return state, action, reward, isOver,
+            note that some frames in state may be generated from last episode,
+            they should be removed from state
+            """
+        state = np.zeros(
+            (self.context_len + 1, ) + self.state_shape, dtype=np.uint8)
+        state_idx = np.arange(idx,
+                              idx + self.context_len + 1) % self._curr_size
+
+        # confirm that no frame was generated from last episode
+        has_last_episode = False
+        for k in range(self.context_len - 2, -1, -1):
+            to_check_idx = state_idx[k]
+            if self.isOver[to_check_idx]:
+                has_last_episode = True
+                state_idx = state_idx[k + 1:]
+                state[k + 1:] = self.state[state_idx]
+                break
+
+        if not has_last_episode:
+            state = self.state[state_idx]
+
+        real_idx = (idx + self.context_len - 1) % self._curr_size
+        action = self.action[real_idx]
+        reward = self.reward[real_idx]
+        isOver = self.isOver[real_idx]
+        return state, reward, action, isOver
+
+    def __len__(self):
+        return self._curr_size
+
+    def _assign(self, pos, exp):
+        self.state[pos] = exp.state
+        self.reward[pos] = exp.reward
+        self.action[pos] = exp.action
+        self.isOver[pos] = exp.isOver
+
+    def sample_batch(self, batch_size):
+        """sample a batch from replay memory for training
+        """
+        batch_idx = np.random.randint(
+            self._curr_size - self.context_len - 1, size=batch_size)
+        batch_idx = (self._curr_pos + batch_idx) % self._curr_size
+        batch_exp = [self.sample(i) for i in batch_idx]
+        return self._process_batch(batch_exp)
+
+    def _process_batch(self, batch_exp):
+        state = np.asarray([e[0] for e in batch_exp], dtype='uint8')
+        reward = np.asarray([e[1] for e in batch_exp], dtype='float32')
+        action = np.asarray([e[2] for e in batch_exp], dtype='int8')
+        isOver = np.asarray([e[3] for e in batch_exp], dtype='bool')
+        return [state, action, reward, isOver]
diff --git a/examples/DQN/rom_files/breakout.bin b/examples/DQN/rom_files/breakout.bin
new file mode 100644
index 0000000000000000000000000000000000000000..abab5a8c0a1890461a11b78d4265f1b794327793
Binary files /dev/null and b/examples/DQN/rom_files/breakout.bin differ
diff --git a/examples/DQN/rom_files/pong.bin b/examples/DQN/rom_files/pong.bin
new file mode 100644
index 0000000000000000000000000000000000000000..14a5bdfc72548613c059938bdf712efdbb5d3806
Binary files /dev/null and b/examples/DQN/rom_files/pong.bin differ
diff --git a/examples/DQN/train.py b/examples/DQN/train.py
new file mode 100644
index 0000000000000000000000000000000000000000..3d2d8d48ccd37be367d346f3acd665eacaae5d37
--- /dev/null
+++ b/examples/DQN/train.py
@@ -0,0 +1,164 @@
+#   Copyright (c) 2018 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 argparse
+import cv2
+import gym
+import paddle.fluid as fluid
+import numpy as np
+import os
+from atari import AtariPlayer
+from atari_agent import AtariAgent
+from atari_model import AtariModel
+from atari_wrapper import FrameStack, MapState, FireResetEnv, LimitLength
+from collections import deque
+from datetime import datetime
+from expreplay import ReplayMemory, Experience
+from parl.algorithms import DQNAlgorithm
+from parl.utils import logger
+from tqdm import tqdm
+
+MEMORY_SIZE = 1e6
+MEMORY_WARMUP_SIZE = MEMORY_SIZE // 20
+IMAGE_SIZE = (84, 84)
+CONTEXT_LEN = 4
+ACTION_REPEAT = 4  # aka FRAME_SKIP
+UPDATE_FREQ = 4
+GAMMA = 0.99
+LEARNING_RATE = 1e-3
+
+
+def run_train_episode(agent, env, exp):
+    total_reward = 0
+    all_cost = []
+    state = env.reset()
+    step = 0
+    while True:
+        step += 1
+        context = exp.recent_state()
+        context.append(state)
+        context = np.stack(context, axis=0)
+        action = agent.sample(context)
+        next_state, reward, isOver, _ = env.step(action)
+        exp.append(Experience(state, action, reward, isOver))
+        # start training
+        if len(exp) > MEMORY_WARMUP_SIZE:
+            if step % UPDATE_FREQ == 0:
+                batch_all_state, batch_action, batch_reward, batch_isOver = exp.sample_batch(
+                    args.batch_size)
+                batch_state = batch_all_state[:, :CONTEXT_LEN, :, :]
+                batch_next_state = batch_all_state[:, 1:, :, :]
+                cost = agent.learn(batch_state, batch_action, batch_reward,
+                                   batch_next_state, batch_isOver)
+                all_cost.append(float(cost))
+        total_reward += reward
+        state = next_state
+        if isOver:
+            break
+    logger.info('[Train]total_reward: {}, mean_cost: {}'.format(
+        total_reward, np.mean(all_cost)))
+    return total_reward, step
+
+
+def get_player(rom, viz=False, train=False):
+    env = AtariPlayer(
+        rom,
+        frame_skip=ACTION_REPEAT,
+        viz=viz,
+        live_lost_as_eoe=train,
+        max_num_frames=60000)
+    env = FireResetEnv(env)
+    env = MapState(env, lambda im: cv2.resize(im, IMAGE_SIZE))
+    if not train:
+        # in training, context is taken care of in expreplay buffer
+        env = FrameStack(env, CONTEXT_LEN)
+    return env
+
+
+def eval_agent(agent, env):
+    episode_reward = []
+    for _ in tqdm(range(30), desc='eval agent'):
+        state = env.reset()
+        total_reward = 0
+        step = 0
+        while True:
+            step += 1
+            action = agent.predict(state)
+            state, reward, isOver, info = env.step(action)
+            total_reward += reward
+            if isOver:
+                break
+        episode_reward.append(total_reward)
+    eval_reward = np.mean(episode_reward)
+    return eval_reward
+
+
+def train_agent():
+    env = get_player(args.rom, train=True)
+    test_env = get_player(args.rom)
+    exp = ReplayMemory(MEMORY_SIZE, IMAGE_SIZE, CONTEXT_LEN)
+    action_dim = env.action_space.n
+
+    hyperparas = {
+        'action_dim': action_dim,
+        'lr': LEARNING_RATE,
+        'gamma': GAMMA
+    }
+    model = AtariModel(IMAGE_SIZE[0], IMAGE_SIZE[1], action_dim)
+    algorithm = DQNAlgorithm(model, hyperparas)
+    agent = AtariAgent(algorithm, action_dim)
+
+    with tqdm(total=MEMORY_WARMUP_SIZE) as pbar:
+        while len(exp) < MEMORY_WARMUP_SIZE:
+            total_reward, step = run_train_episode(agent, env, exp)
+            pbar.update(step)
+
+    # train
+    test_flag = 0
+    pbar = tqdm(total=1e8)
+    recent_100_reward = []
+    total_step = 0
+    max_reward = None
+    while True:
+        # start epoch
+        total_reward, step = run_train_episode(agent, env, exp)
+        total_step += step
+        pbar.set_description('[train]exploration:{}'.format(agent.exploration))
+        pbar.update(step)
+
+        if total_step // args.test_every_steps == test_flag:
+            pbar.write("testing")
+            eval_reward = eval_agent(agent, test_env)
+            test_flag += 1
+            logger.info(
+                "eval_agent done, (steps, eval_reward): ({}, {})".format(
+                    total_step, eval_reward))
+
+    pbar.close()
+
+
+if __name__ == '__main__':
+    parser = argparse.ArgumentParser()
+    parser.add_argument('--rom', help='atari rom', required=True)
+    parser.add_argument(
+        '--use_cuda', action='store_true', help='if set, use cuda')
+    parser.add_argument(
+        '--batch_size', type=int, default=64, help='batch size for training')
+    parser.add_argument(
+        '--test_every_steps',
+        type=int,
+        default=100000,
+        help='every steps number to run test')
+    args = parser.parse_args()
+    train_agent()
diff --git a/parl/algorithms/__init__.py b/parl/algorithms/__init__.py
new file mode 100644
index 0000000000000000000000000000000000000000..e665bc49297fd637fe53df9b6222ab991b0b0576
--- /dev/null
+++ b/parl/algorithms/__init__.py
@@ -0,0 +1,14 @@
+#   Copyright (c) 2018 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 parl.algorithms.dqn_algorithm import *
diff --git a/parl/algorithms/dqn_algorithm.py b/parl/algorithms/dqn_algorithm.py
new file mode 100644
index 0000000000000000000000000000000000000000..3088a8128241c26bedc35daa782dfaba6d9ba50f
--- /dev/null
+++ b/parl/algorithms/dqn_algorithm.py
@@ -0,0 +1,58 @@
+#   Copyright (c) 2018 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.fluid as fluid
+from parl.framework.algorithm_base import Algorithm
+import parl.layers as layers
+import copy
+
+
+class DQNAlgorithm(Algorithm):
+    def __init__(self, model, hyperparas):
+        Algorithm.__init__(self, model, hyperparas)
+        self.model = model
+        self.target_model = copy.deepcopy(model)
+        # fetch hyper parameters
+        self.action_dim = hyperparas['action_dim']
+        self.gamma = hyperparas['gamma']
+        self.lr = hyperparas['lr']
+
+    def define_predict(self, obs):
+        return self.model.value(obs)
+
+    def define_learn(self, obs, action, reward, next_obs, terminal):
+        pred_value = self.model.value(obs)
+        #fluid.layers.Print(pred_value, summarize=10, message='pred_value')
+        next_pred_value = self.target_model.value(next_obs)
+        #fluid.layers.Print(next_pred_value, summarize=10, message='next_pred_value')
+        best_v = layers.reduce_max(next_pred_value, dim=1)
+        best_v.stop_gradient = True
+        #fluid.layers.Print(best_v, summarize=10, message='best_v')
+        target = reward + (
+            1.0 - layers.cast(terminal, dtype='float32')) * self.gamma * best_v
+
+        #fluid.layers.Print(target, summarize=10, message='target')
+        action_onehot = layers.one_hot(action, self.action_dim)
+        action_onehot = layers.cast(action_onehot, dtype='float32')
+        pred_action_value = layers.reduce_sum(
+            layers.elementwise_mul(action_onehot, pred_value), dim=1)
+        #fluid.layers.Print(pred_action_value, summarize=10, message='pred_action_value')
+        cost = layers.square_error_cost(pred_action_value, target)
+        cost = layers.reduce_mean(cost)
+        optimizer = fluid.optimizer.Adam(self.lr * 0.5, epsilon=1e-3)
+        optimizer.minimize(cost)
+        return cost
+
+    def sync_target(self, gpu_id):
+        self.model.sync_params_to(self.target_model, gpu_id=gpu_id)
diff --git a/parl/framework/agent_base.py b/parl/framework/agent_base.py
index 3c3232792840837f17dc68248f9aede1b6b50623..6fbe81d6c744ae2cfd00b98f8d5372bac8e4e6de 100644
--- a/parl/framework/agent_base.py
+++ b/parl/framework/agent_base.py
@@ -16,6 +16,7 @@ import paddle.fluid as fluid
 import parl.layers as layers
 from parl.framework.algorithm_base import Algorithm
 from parl.framework.model_base import Model
+from parl.utils import get_gpu_count
 
 __all__ = ['Agent']
 
@@ -31,10 +32,23 @@ class Agent(object):
     c. define a Agent with the algorithm
     """
 
-    def __init__(self, algorithm):
+    def __init__(self, algorithm, gpu_id=None):
+        """ build program and run initialization for default_startup_program
+        
+        Created object:
+            self.alg: parl.framework.Algorithm
+            self.gpu_id: int
+            self.fluid_executor: fluid.Executor
+        """
         assert isinstance(algorithm, Algorithm)
         self.alg = algorithm
+
         self.build_program()
+
+        if gpu_id is None:
+            gpu_id = 0 if get_gpu_count() > 0 else -1
+        self.gpu_id = gpu_id
+        place = fluid.CUDAPlace(gpu_id) if gpu_id >= 0 else fluid.CPUPlace()
         self.fluid_executor = fluid.Executor(place)
         self.fluid_executor.run(fluid.default_startup_program())
 
diff --git a/parl/framework/tests/agent_base_test.py b/parl/framework/tests/agent_base_test.py
new file mode 100644
index 0000000000000000000000000000000000000000..f00485aeaf80308c57ac3e8a894a609b848467cc
--- /dev/null
+++ b/parl/framework/tests/agent_base_test.py
@@ -0,0 +1,83 @@
+#   Copyright (c) 2018 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 numpy as np
+import parl.layers as layers
+import unittest
+from paddle import fluid
+from parl.framework.agent_base import Agent
+from parl.framework.algorithm_base import Algorithm
+from parl.framework.model_base import Model
+from parl.utils import gputils
+
+
+class TestModel(Model):
+    def __init__(self):
+        self.fc1 = layers.fc(size=256)
+        self.fc2 = layers.fc(size=128)
+
+    def policy(self, obs):
+        out = self.fc1(obs)
+        out = self.fc2(out)
+        return out
+
+
+class TestAlgorithm(Algorithm):
+    def __init__(self, model, hyperparas=None):
+        super(TestAlgorithm, self).__init__(model, hyperparas)
+
+    def define_predict(self, obs):
+        return self.model.policy(obs)
+
+
+class TestAgent(Agent):
+    def __init__(self, algorithm, gpu_id=None):
+        super(TestAgent, self).__init__(algorithm, gpu_id)
+
+    def build_program(self):
+        self.predict_program = fluid.Program()
+        with fluid.program_guard(self.predict_program):
+            obs = layers.data(name='obs', shape=[10], dtype='float32')
+            output = self.alg.define_predict(obs)
+        self.predict_output = [output]
+
+    def predict(self, obs):
+        output_np = self.fluid_executor.run(
+            self.predict_program,
+            feed={'obs': obs},
+            fetch_list=self.predict_output)[0]
+        return output_np
+
+
+class AgentBaseTest(unittest.TestCase):
+    def setUp(self):
+        self.model = TestModel()
+        self.algorithm = TestAlgorithm(self.model)
+
+    def test_agent_with_gpu(self):
+        if gputils.get_gpu_count() > 0:
+            agent = TestAgent(self.algorithm, gpu_id=0)
+            obs = np.random.random([3, 10]).astype('float32')
+            output_np = agent.predict(obs)
+            self.assertIsNotNone(output_np)
+
+    def test_agent_with_cpu(self):
+        agent = TestAgent(self.algorithm, gpu_id=0)
+        obs = np.random.random([3, 10]).astype('float32')
+        output_np = agent.predict(obs)
+        self.assertIsNotNone(output_np)
+
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/parl/utils/gputils.py b/parl/utils/gputils.py
index 60b6b84860ea79b229a3220f6ca413acbcdb8d0c..e0056b5e08209d9009db65de975ddf6bccc42378 100644
--- a/parl/utils/gputils.py
+++ b/parl/utils/gputils.py
@@ -31,15 +31,20 @@ def get_gpu_count():
     env_cuda_devices = os.environ.get('CUDA_VISIBLE_DEVICES', None)
     if env_cuda_devices is not None:
         assert isinstance(env_cuda_devices, str)
-        gpu_count = len(env_cuda_devices.split(','))
-        logger.info(
-            'CUDA_VISIBLE_DEVICES found gpu count: {}'.format(gpu_count))
+        try:
+            gpu_count = len(
+                [x for x in env_cuda_devices.split(',') if int(x) >= 0])
+            logger.info(
+                'CUDA_VISIBLE_DEVICES found gpu count: {}'.format(gpu_count))
+        except Exception as e:
+            logger.error(e.message)
+            gpu_count = 0
     else:
         try:
             gpu_count = str(subprocess.check_output(["nvidia-smi",
                                                      "-L"])).count('UUID')
             logger.info('nvidia-smi -L found gpu count: {}'.format(gpu_count))
         except Exception as e:
-            logger.warn(e.message)
+            logger.error(e.message)
             gpu_count = 0
     return gpu_count