A security authentication for PC client is provided according to the present invention, wherein said method includes: PC client sends a registry request to a server with a user ID and a password; The server makes first authentication based on the user ID and password, if the authentication succeeds, a field used for re-authentication will be created and returned to the PC client through an authentication successful message; When initiating a call, the PC client transmits the user ID and the field used for re-authentication acquired when registered to media gateway controller; The media gateway controller transfers the user ID and field used for re-authentication to the server, which makes second authentication according to the user ID and the field used for the second authentication, if the authentication fails, the call will be rejected, otherwise the call will be accepted and returns information of the called subscriber. The present invention successfully associates call and subscriber registry together, preferably solves security problems of the having registered legal PC subscriber and largely improves security performance when the subscriber uses the resources.