diff --git a/torchquantum/algorithm/qcbm.py b/torchquantum/algorithm/qcbm.py
index c0b6e5e3..12a63dfb 100644
--- a/torchquantum/algorithm/qcbm.py
+++ b/torchquantum/algorithm/qcbm.py
@@ -46,7 +46,7 @@ def forward(self, px, py):
         """
         Squared MMD loss.
     Args:
-        px: First probability distribution
+            px: First probability distribution
         py: Second probability distribution
 
         Returns: