We discuss the security of the kind of multiparty quantum secret sharing protocols encrypting in series. It is secure against the eavesdroppers outside. However it is weak to withstand the attack of insider with a fake signal and cheating. An idiographic attack strategy is given based on the protocol. Furthermore, we conclude the key leak of the protocols and present a possible way to prevent the dishonest agents from stealing the secret. It is secure against the eavesdroppers outside. However it is weak to withstand the attack of insider with a fake signal and cheating. An idiographic attack strategy is given based on the protocol. Furthermore, we conclude the key leak of the protocols and present a possible way to prevent the dishonest agents from stealing the secret.