diff --git a/paddle/framework/ddim.cc b/paddle/framework/ddim.cc
index 73f5499ad15752237a73ca27e0cd0fe2c5e86b4e..b6ad8b60aaf7b5657e1f18defe3c8d2c2ebbc060 100644
--- a/paddle/framework/ddim.cc
+++ b/paddle/framework/ddim.cc
@@ -117,6 +117,8 @@ int DDim::operator[](int idx) const {
   return boost::apply_visitor(DynamicConstIndexer(idx), var);
 }
 
+ssize_t DDim::size() const { return arity(*this); }
+
 bool DDim::operator==(DDim d) const {
   if (var.which() != d.getVar().which()) {
     return false;
diff --git a/paddle/framework/ddim.h b/paddle/framework/ddim.h
index a0c2a8a74afdefd4a504ec6fa730238e077efbb5..7bc21a1e3455bcf8889c18084e8c96e7a3c76a13 100644
--- a/paddle/framework/ddim.h
+++ b/paddle/framework/ddim.h
@@ -50,6 +50,8 @@ struct DDim {
 
   DDimVar getVar() { return var; }
 
+  ssize_t size() const;
+
   bool operator==(DDim d) const;
 
   bool operator!=(DDim d) const;
diff --git a/paddle/framework/ddim_test.cc b/paddle/framework/ddim_test.cc
index 6a099f2aeb4aa117bca8695aa326fbd1272a43d6..9d18a2972ce62139430b240b4599854b14290a32 100644
--- a/paddle/framework/ddim_test.cc
+++ b/paddle/framework/ddim_test.cc
@@ -49,6 +49,7 @@ TEST(DDim, Equality) {
 
   // arity of a DDim
   EXPECT_EQ(paddle::framework::arity(ddim), 3);
+  EXPECT_EQ(ddim.size(), 3);
 
   // product of a DDim
   EXPECT_EQ(paddle::framework::product(vddim), 45);