diff --git a/qlib/data/ops.py b/qlib/data/ops.py
index e17c0e4e6..72cfa4520 100644
--- a/qlib/data/ops.py
+++ b/qlib/data/ops.py
@@ -143,6 +143,11 @@ class Sign(ElemOperator):
     def __init__(self, feature):
         super(Sign, self).__init__(feature, "sign")
 
+    def _load_internal(self, instrument, start_index, end_index, freq):
+        series = self.feature.load(instrument, start_index, end_index, freq)
+        series = series.astype(np.float32)
+        return getattr(np, self.func)(series)
+
 
 class Log(ElemOperator):
     """Feature Log