A system and a method for security authentication, in which a biometric authentication subsystem in the security authentication system receives a biometric certificate held by the user and the user's biometric information from a user terminal; the biometric certificate contains the user's biometric template or the storage address of the biometric template; next, the biometric authentication subsystem authenticates the biometric certificate, performs matching between the biometric information and the biometric template, and generates the identity authentication result. The invention can also combine biometric authentication with PMI privilege authentication, so as to enhance security of identity authentication in PMI and widen applicability of biometric authentication.