diff --git a/index.js b/index.js
index 5b82276..56d86b5 100644
--- a/index.js
+++ b/index.js
@@ -622,7 +622,7 @@ module.exports = {
   distanceSig(hash, sig){ // hash为64hex字符，sig为128hex字符。返回用hex表达的距离。
     if (this.isSignature(sig) && this.isHash(hash)){
       var hashSig=this.hash(sig) // 把签名也转成32字节的哈希，同样长度方便比较
-      return new BigInt(hash,16).sub(new BigInt(hashSig,16)).abs().toString(16)
+      return new BigInt(hash,16).subtract(new BigInt(hashSig,16)).abs().toString(16)
     }
     return null
   }