diff --git a/qlib/data/ops.py b/qlib/data/ops.py
index d9a2ffbb3e3..671948d98cf 100644
--- a/qlib/data/ops.py
+++ b/qlib/data/ops.py
@@ -1337,7 +1337,7 @@ def _load_internal(self, instrument, start_index, end_index, *args):
         def weighted_mean(x):
             w = np.arange(len(x)) + 1
             w = w / w.sum()
-            return np.nanmean(w * x)
+            return np.nansum(w * x)
 
         if self.N == 0:
             series = series.expanding(min_periods=1).apply(weighted_mean, raw=True)
diff --git a/tests/ops/test_rolling_ops.py b/tests/ops/test_rolling_ops.py
new file mode 100644
index 00000000000..a6e46600b43
--- /dev/null
+++ b/tests/ops/test_rolling_ops.py
@@ -0,0 +1,20 @@
+import numpy as np
+import pandas as pd
+
+from qlib.data.ops import WMA
+
+
+class _Feature:
+    def __init__(self, series):
+        self.series = series
+
+    def load(self, *args):
+        return self.series
+
+
+def test_wma_uses_weighted_sum():
+    series = pd.Series([1.0, 2.0, 3.0])
+
+    result = WMA(_Feature(series), 3)._load_internal("SH600000", 0, 2)
+
+    np.testing.assert_allclose(result.to_numpy(), [1.0, 5.0 / 3.0, 14.0 / 6.0])