diff --git a/paddle/operators/sgd_op.cc b/paddle/operators/sgd_op.cc
index 72f4e4d5cbcd692423fa2a3e9ec8e7033b552c3c..5576d7b8be060a3c58cb18ed667041562cf853b8 100644
--- a/paddle/operators/sgd_op.cc
+++ b/paddle/operators/sgd_op.cc
@@ -55,7 +55,7 @@ SGD operator
 
 This operator implements one step of the stochastic gradient descent algorithm.
 
-$$param_out = param - learning_rate * grad$$
+$$param\_out = param - learning\_rate * grad$$
 
 )DOC");
   }