The invention provides a method, a system and a device for mutual authentication. The method comprises: a network entity obtains the new triplet vector of mobile equipment (ME); according to the triplet vector, the network entity generates an output parameter and sends the output parameter to the ME, wherein the output parameter is formed by encrypting random number RAND and authentication execution time CNR; the ME decrypts the output parameter and authenticates the network according to a decrypting result; meanwhile, the a subscriber identity module (SIM) card of the ME generates an RES and sends the generated RES to the network entity; and the network entity authenticates the ME according to the received RES. The invention can realize mutual authentication between ME and the network side and can judge that ME authenticates the network not to pass when suffering replay attack.