diff --git a/paddle/framework/ddim.cc b/paddle/framework/ddim.cc
index 58e20625ce7a3d71e4fc59dc5478539eecd6b88c..fc3d508553c0e966978b28d58127bdbff10d45f1 100644
--- a/paddle/framework/ddim.cc
+++ b/paddle/framework/ddim.cc
@@ -284,8 +284,6 @@ DDim::DDim(std::initializer_list<int64_t> init_list) {
   *this = make_ddim(init_list);
 }
 
-// Reshape a tensor to a matrix. The matrix's first dimension(column length)
-// will be the product of tensor's first `num_col_dims` dimensions
 DDim flatten_to_2d(const DDim& src, int num_col_dims) {
   int rank = src.size();
   return make_ddim({product(slice_ddim(src, 0, num_col_dims)),
diff --git a/paddle/framework/ddim.h b/paddle/framework/ddim.h
index 1e7ca46bd98d3c8b49c042101b68277572b7de72..48e14d16e3ef4c04ec5c6a1a4f3fcd997b9672c0 100644
--- a/paddle/framework/ddim.h
+++ b/paddle/framework/ddim.h
@@ -115,6 +115,8 @@ int arity(const DDim& ddim);
 
 std::ostream& operator<<(std::ostream&, const DDim&);
 
+// Reshape a tensor to a matrix. The matrix's first dimension(column length)
+// will be the product of tensor's first `num_col_dims` dimensions
 DDim flatten_to_2d(const DDim& src, int num_col_dims);
 
 DDim flatten_to_1d(const DDim& src);