diff --git a/docs/operators/ALiBiMask.md b/docs/operators/ALiBiMask.md
index afdc3a3..33eca0f 100644
--- a/docs/operators/ALiBiMask.md
+++ b/docs/operators/ALiBiMask.md
@@ -22,7 +22,7 @@ The following code shows the calculation process of mask.
 alibi_mask = torch.full((seqlen_q, seqlen_kv), float('inf'), dtype=data_type)
 for i in range(seqlen_q-1, -1, -1):
     for j in range(seqlen_kv):
-        mask = j - seqlen_kv + 1 + (seqlen_q - 1 - i)
+        mask = j - i + (seqlen_q - seqlen_kv)
         if mask <= 0:
             alibi_mask[i][j] = mask
 alibi_mask = alibi_mask.unsqueeze(0).expand(num_heads, -1, -1)