diff --git a/paddle/framework/backward.cc b/paddle/framework/backward.cc
index 7b470adb47f63d855ec784e9b2765e7fe0fc3ae6..dae457f858593f476cb0973b7bc119e546f12c79 100644
--- a/paddle/framework/backward.cc
+++ b/paddle/framework/backward.cc
@@ -49,11 +49,9 @@ static std::shared_ptr<OperatorBase> EmptyOp() {
   return net_op;
 }
 
-static void DeDuplicate(NetOp* net, std::unordered_se)
-
-    static std::shared_ptr<OperatorBase> BackwardImpl(
-        const OperatorBase& forwardOp,
-        std::unordered_set<std::string>& no_grad_names, unsigned& uniq_id) {
+static std::shared_ptr<OperatorBase> BackwardImpl(
+    const OperatorBase& forwardOp,
+    std::unordered_set<std::string>& no_grad_names, size_t& uniq_id) {
   if (AllInSet(forwardOp.inputs_, OperatorBase::GRAD_VAR_SUFFIX(),
                no_grad_names)) {
     return EmptyOp();
@@ -73,13 +71,16 @@ static void DeDuplicate(NetOp* net, std::unordered_se)
   if (forwardOp.IsNetOp()) {
     //! TODO(dzh)
     std::unordered_map<std::string, int> dup_output;
-    std::unordered_map<std::string std::vector<int>> dup_output_ops;
-    const unsigned uniq_id_local = uniq_id;
-    unsigned op_id_offset = 0;
-    for (auto& fwd : forwardOp) {
-      auto bwd = Backward(fwd, no_grad_names);
+    std::unordered_map<std::string, std::vector<int>> dup_output_ops;
+    //    const unsigned uniq_id_local = uniq_id;
+    int op_id_offset = 0;
+    // Because it is a net op, it can static_cast.
+    auto& forwardNet = static_cast<const NetOp&>(forwardOp);
+
+    for (auto& fwd : forwardNet.ops_) {
+      auto bwd = Backward(*fwd, no_grad_names);
       net->AddOp(bwd);
-      for (size_t i = 0; i < bwd.outputs_; ++i) {
+      for (size_t i = 0; i < bwd->outputs_.size(); ++i) {
         bwd->outputs_[i] += OperatorBase::EMPTY_VAR_NAME();
         if (dup_output.find(bwd->inputs_[i]) == dup_output.end()) {
           dup_output[bwd->inputs_[i]] = 1;
@@ -138,7 +139,7 @@ extern std::shared_ptr<OperatorBase> Backward(
   for (auto& name : no_grad_vars) {
     no_grad_names.insert(name + OperatorBase::GRAD_VAR_SUFFIX());
   }
-  int uid = 0;
+  size_t uid = 0;
   return BackwardImpl(forwardOp, no_grad_names, uid);
 }
 }  // namespace framework