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Arbitrated quantum signature (AQS) is an important branch in quantum cryptography to authenticate quantum information,and cryptanalysis on AQS protocols helps to evaluate and improve security of AQS.Recently,it is discovered that an AQS protocol based on chained controlled-NOT (CNOT) algorithm is vulnerable to a novel attack because a transformation from binary keys into permutations and the chained CNOT algorithm have special properties,which enables a malicious receiver to forge signatures with probability 1/2.Moreover,a malicious signer can also deny his signatures with probability 1/4.Then,two possible improved methods are presented to resist these attacks:one is padding constants to reduce probability of the successful attacks,and the other is a circular chained CNOT algorithm to make the attack strategy invalid.And the security analysis shows that both the two improve methods could well resist these attacks.