The invention provides an authentication method and a system of a subscriber identity module and a terminal. The method comprises the following steps: after judging that an authentication key between self and the terminal is required to be obtained, the subscriber identity module sends key updating request to a key management system platform carrying identifiers of the subscriber identity module and the terminal; after receiving the key updating request, the key management system platform generates a message carrying the authentication key according to the identifier of the terminal and determines a transmission key corresponding to the identifier of the subscriber identity module; the transmission key and transmission encryption and decryption algorithm are used for encrypting the messagecarrying the authentication key and then sending the message to the subscriber identity module; the subscriber identity module uses the prestored transmission key and the transmission encryption anddecryption algorithm to decrypt the message and obtains and stores the authentication key according to the decrypted message; the authentication key is prestored in the terminal, or is obtained according to the decrypted message; the subscriber identity module and the terminal use the authentication key and authentication encryption and decryption algorithm for mutual authentication.