diff --git a/mmengine/model/averaged_model.py b/mmengine/model/averaged_model.py
index ab9ab9c0ea49e8fd6659b053be2a6fc58fc5bced..e2f75e99d4dc9979be9d862367f775bee0c9f50d 100644
--- a/mmengine/model/averaged_model.py
+++ b/mmengine/model/averaged_model.py
@@ -129,7 +129,7 @@ class StochasticWeightAverage(BaseAveragedModel):
         """
         averaged_param.add_(
             source_param - averaged_param,
-            alpha=1 / (steps // self.interval + 1))
+            alpha=1 / float(steps // self.interval + 1))
 
 
 @MODELS.register_module()