diff --git a/imperative/python/megengine/functional/nn.py b/imperative/python/megengine/functional/nn.py
index 46cf27711d37261d0ffaed30e04bac8385b2ff13..ebcdbbcbf865e5f4bc353ac0712dc053ec6bba9f 100644
--- a/imperative/python/megengine/functional/nn.py
+++ b/imperative/python/megengine/functional/nn.py
@@ -1090,6 +1090,9 @@ def layer_norm(
         eps_mode
     )
 
+    if amp._enabled:
+        inp, weight, bias = cast_tensors(inp, weight, bias, promote=True)
+
     _device = inp.device
     _dtype = inp.dtype
     _dim = len(inp.shape) - len(normalized_shape)