diff --git a/kws/utils/executor.py b/kws/utils/executor.py
index 51fc529..d30fb0a 100644
--- a/kws/utils/executor.py
+++ b/kws/utils/executor.py
@@ -46,6 +46,7 @@ class Executor:
             logits = model(feats)
             loss_type = args.get('criterion', 'max_pooling')
             loss, acc = criterion(loss_type, logits, target, feats_lengths)
+            optimizer.zero_grad()
             loss.backward()
             grad_norm = clip_grad_norm_(model.parameters(), clip)
             if torch.isfinite(grad_norm):