diff --git a/paddle/operators/smooth_l1_loss_op.cc b/paddle/operators/smooth_l1_loss_op.cc
index d2c6d955a72d46ddbb2b5533378e2aca4f2cc929..5c704c35b444b5aad8d86dcee2f4ae3a2fd830d4 100644
--- a/paddle/operators/smooth_l1_loss_op.cc
+++ b/paddle/operators/smooth_l1_loss_op.cc
@@ -70,14 +70,14 @@ class SmoothL1LossOpMaker : public framework::OpProtoAndCheckerMaker {
     AddOutput("diff", "Intermediate variable to cache Win*(X-Y).")
         .AsIntermediate();
     AddOutput("Out", "Final smooth l1 loss of inputs.");
+    AddAttr<AttrType>("sigma", "Hyper parameter, default value is 3.0 .")
+        .SetDefault(3.0);
     AddComment(R"DOC(
 Compute SmoothL1Loss for input and target.
-
-The equation is: Out = 0.5 * (sigma * (X - Y)) ^ 2  if abs(X - Y) < 1 / sigma^2
-                       abs(X - Y) - 0.5 / sigma^2   otherwise
+The equation is:
+loss = 0.5 * (sigma * (x - y)) ^ 2 if abs(x - y) < 1 / sigma^2
+       abs(x - y) - 0.5 / sigma^2  otherwise
 )DOC");
-    AddAttr<AttrType>("sigma", "Hyper parameter, default value is 3.0 .")
-        .SetDefault(3.0);
   }
 };