diff --git a/paddlespeech/s2t/exps/u2/model.py b/paddlespeech/s2t/exps/u2/model.py
index 66b95f63..1d813761 100644
--- a/paddlespeech/s2t/exps/u2/model.py
+++ b/paddlespeech/s2t/exps/u2/model.py
@@ -492,10 +492,9 @@ class U2Tester(U2Trainer):
         ]
         infer_model.forward_encoder_chunk = paddle.jit.to_static(
             infer_model.forward_encoder_chunk, input_spec=input_spec)
-        # paddle.jit.save(static_model, self.args.export_path, combine_params=True)
 
         ######################### infer_model.forward_attention_decoder ########################
-        # TODO: 512(encoder_output) be configable. 1 for B
+        # TODO: 512(encoder_output) be configable. 1 for BatchSize
         input_spec = [
             paddle.static.InputSpec(shape=[None, None], dtype='int64'),
             paddle.static.InputSpec(shape=[None], dtype='int64'),
@@ -503,7 +502,6 @@ class U2Tester(U2Trainer):
         ]
         infer_model.forward_attention_decoder = paddle.jit.to_static(
             infer_model.forward_attention_decoder, input_spec=input_spec)
-        # paddle.jit.save(static_model, self.args.export_path, combine_params=True)
 
         ######################### infer_model.ctc_activation ########################
         # TODO: 512(encoder_output) be configable
@@ -513,8 +511,10 @@ class U2Tester(U2Trainer):
         infer_model.ctc_activation = paddle.jit.to_static(
             infer_model.ctc_activation, input_spec=input_spec)
 
-        paddle.jit.save(infer_model, './export.jit', combine_params=True, skip_forward=True)
+        # jit save
+        paddle.jit.save(infer_model, self.args.export_path, combine_params=True, skip_forward=True)
 
+        # test dy2static
         def flatten(out):
             if isinstance(out, paddle.Tensor):
                 return [out]
@@ -541,7 +541,7 @@ class U2Tester(U2Trainer):
 
         from paddle.jit.layer import Layer
         layer = Layer()
-        layer.load('./export.jit', paddle.CPUPlace())
+        layer.load(self.args.export_path, paddle.CPUPlace())
 
         xs1 = paddle.full([1, 7, 80], 0.1, dtype='float32')
         offset = paddle.to_tensor([0], dtype='int32')
diff --git a/paddlespeech/s2t/modules/encoder.py b/paddlespeech/s2t/modules/encoder.py
index a7919bca..230894d5 100644
--- a/paddlespeech/s2t/modules/encoder.py
+++ b/paddlespeech/s2t/modules/encoder.py
@@ -251,7 +251,12 @@ class BaseEncoder(nn.Layer):
         for i, layer in enumerate(self.encoders):
             # att_cache[i:i+1] = (1, head, cache_t1, d_k*2)
             # cnn_cache[i:i+1] = (1, B=1, hidden-dim, cache_t2)
-            # zeros([0,0,0,0]) support [i:i+1] slice
+
+            # WARNING: eliminate if-else cond op in graph
+            # tensor zeros([0,0,0,0]) support [i:i+1] slice, will return zeros([0,0,0,0]) tensor
+            # raw code as below:
+            #   att_cache=att_cache[i:i+1] if elayers > 0 else att_cache,
+            #   cnn_cache=cnn_cache[i:i+1] if paddle.shape(cnn_cache)[0] > 0 else cnn_cache,
             xs, _, new_att_cache, new_cnn_cache = layer(
                 xs, att_mask, pos_emb,
                 att_cache=att_cache[i:i+1],