diff --git a/paddle/parameter/ParameterUpdaterHook.cpp b/paddle/parameter/ParameterUpdaterHook.cpp
index e29494868bc3b4ca39e95541771c727ec2ffef81..5e8c77ced03f5547f3d1145b1c7c4900a5223087 100644
--- a/paddle/parameter/ParameterUpdaterHook.cpp
+++ b/paddle/parameter/ParameterUpdaterHook.cpp
@@ -30,9 +30,9 @@ namespace paddle {
 
 /**
  * The static pruning hook
- * Static means user specific a sparsity_ratio map before training started. The
- * network will
- * hold the sparsity_ratio maximum numbers of parameters, and cut off the rest.
+ * Static means user specific a sparsity_ratio before training start, and the
+ * network will prune the parameters based on the sparsity_ratio. More deatils
+ * can see https://arxiv.org/pdf/1506.02626.pdf.
  */
 
 class StaticPruningHook : public IParameterUpdaterHook {
diff --git a/proto/ParameterConfig.proto b/proto/ParameterConfig.proto
index 53e3b94f031c3bd4967cd031cb362442754901f3..360342bac6facf47b91ff1424eecbf3b5b6ae71a 100644
--- a/proto/ParameterConfig.proto
+++ b/proto/ParameterConfig.proto
@@ -25,9 +25,9 @@ enum ParameterInitStrategy {
 }
 
 message ParameterUpdaterHookConfig {
+  // hook type such as  'pruning'
   required string type = 1;
-  //hook type such as  'pruning'
-  optional double sparsity_ratio = 3;
+  optional double sparsity_ratio = 2 [default = 0.8];
 }
 
 message ParameterConfig {
diff --git a/python/paddle/trainer_config_helpers/attrs.py b/python/paddle/trainer_config_helpers/attrs.py
index a0ad8c4452521f394395c72ca9025694c484b525..556701ca7a88c595c4c16fe5b24ccd5b72ae887d 100644
--- a/python/paddle/trainer_config_helpers/attrs.py
+++ b/python/paddle/trainer_config_helpers/attrs.py
@@ -59,17 +59,14 @@ def is_compatible_with(x, Type):
 class HookAttribute(object):
     """
     Hook Attribute object. The hook is an auxiliary operation that occurs 
-    during network propagation. Such as pruning operation, It will cut off 
-    redundant parameters in the network before training. More detail can see 
-    here paddle/parameter/ParameterUpdaterHook.cpp
+    during network propagation.
     NOTE: IT IS A HIGH LEVEL USER INTERFACE.
-		
+
     :param  type: Hook type, eg: 'pruning'
     :type type: string
 
-    :param sparsity_ratio: Must be specified if hook type is 'pruning',
-	                       the network will hold the sparsity_ratio maximum parameters, and cut off the rest. 
-    :type sparsity_ratio: float number between 0 and 1
+    :param sparsity_ratio: Must be specified if hook type is 'pruning'
+    :type sparsity_ratio: float or None
 	
     """