diff --git a/README.cn.md b/README.cn.md
index ff206c8491e5ae9f4d9bda99edb8e579b81525c3..99cba49478dffffcb62d3a4f89f14a8bca2d12ab 100644
--- a/README.cn.md
+++ b/README.cn.md
@@ -72,6 +72,7 @@ pip install parl
 # 算法示例
 - [QuickStart](examples/QuickStart/)
 - [DQN](examples/DQN/)
+- [ES(深度进化算法)](examples/ES/)
 - [DDPG](examples/DDPG/)
 - [PPO](examples/PPO/)
 - [IMPALA](examples/IMPALA/)
diff --git a/README.md b/README.md
index e2327bf58330f9d33ad064b0d8cd807af17ae871..a17d05793a0b93172a7661fe8c647cd443c6a7bf 100644
--- a/README.md
+++ b/README.md
@@ -75,6 +75,7 @@ pip install parl
 # Examples
 - [QuickStart](examples/QuickStart/)
 - [DQN](examples/DQN/)
+- [ES](examples/ES/)
 - [DDPG](examples/DDPG/)
 - [PPO](examples/PPO/)
 - [IMPALA](examples/IMPALA/)
diff --git a/examples/ES/mujoco_agent.py b/examples/ES/mujoco_agent.py
index 58260d7495a23c4f08085895eb6a5158813a6c83..f914e4947528a1fc44bfc0ff965aeb9806bc8121 100644
--- a/examples/ES/mujoco_agent.py
+++ b/examples/ES/mujoco_agent.py
@@ -55,7 +55,7 @@ class MujocoAgent(parl.Agent):
             noises(np.float32): [batch_size, weights_total_size]
         """
 
-        g, count = utils.batched_weighted_sum(
+        g = utils.batched_weighted_sum(
             # mirrored sampling: evaluate pairs of perturbations \epsilon, −\epsilon
             noisy_rewards[:, 0] - noisy_rewards[:, 1],
             noises,
diff --git a/examples/ES/utils.py b/examples/ES/utils.py
index 29d43e02a7f1772e604b57ae2d086651a5a4d266..265da51a77c95856e9b1f156782631b0e51c6480 100644
--- a/examples/ES/utils.py
+++ b/examples/ES/utils.py
@@ -19,6 +19,10 @@ def compute_ranks(x):
 
 
 def compute_centered_ranks(x):
+    """Return ranks that is normliazed to [-0.5, 0.5] with the rewards as input.
+    Args:
+        x(np.array): an array of rewards.
+    """
     y = compute_ranks(x.ravel()).reshape(x.shape).astype(np.float32)
     y /= (x.size - 1)
     y -= 0.5
@@ -26,6 +30,7 @@ def compute_centered_ranks(x):
 
 
 def itergroups(items, group_size):
+    """An iterator that iterates a list with batch data."""
     assert group_size >= 1
     group = []
     for x in items:
@@ -38,16 +43,22 @@ def itergroups(items, group_size):
 
 
 def batched_weighted_sum(weights, vecs, batch_size):
+    """Compute the gradients for updating the parameters.
+    Args:
+        weights(np.array): the nomalized rewards computed by the function `compute_centered_ranks`.
+        vecs(np.array): the noise added to the parameters.
+        batch_size(int): the batch_size for speeding up the computation.
+    Return:
+    total(np.array): aggregated gradient. 
+    """
     total = 0
-    num_items_summed = 0
     for batch_weights, batch_vecs in zip(
             itergroups(weights, batch_size), itergroups(vecs, batch_size)):
         assert len(batch_weights) == len(batch_vecs) <= batch_size
         total += np.dot(
             np.asarray(batch_weights, dtype=np.float32),
             np.asarray(batch_vecs, dtype=np.float32))
-        num_items_summed += len(batch_weights)
-    return total, num_items_summed
+    return total
 
 
 def unflatten(flat_array, array_shapes):
diff --git a/parl/algorithms/__init__.py b/parl/algorithms/__init__.py
index 20c3d3d467cf50b4fed42a7d1b37671b107f1e4b..8565455c374db1e16e878b3977f3c8f2f7c5557d 100644
--- a/parl/algorithms/__init__.py
+++ b/parl/algorithms/__init__.py
@@ -13,8 +13,13 @@
 # limitations under the License.
 
 from parl.utils.utils import _HAS_FLUID, _HAS_TORCH
+from parl.utils import logger
 
 if _HAS_FLUID:
     from parl.algorithms.fluid import *
 elif _HAS_TORCH:
     from parl.algorithms.torch import *
+else:
+    logger.warning(
+        "No deep learning framework was found, but it's ok for parallel computation."
+    )