The invention relates to an identity management system, which comprises an interface module, an exhibition module, an identity combined database and an identify query module, wherein the interface module is used for performing information interaction with other systems; the exhibition module is used for providing exhibition pages, receiving user request messages from users, and returning processing results to the users; the identity combined database is used for storing mapping relations of a plurality of identities of the users; and the identity query module is used for retrieving the identity combined database according to service provider SP identities and user identities and acquiring and returning corresponding identity information. The invention also relates to an identity authentication system, which comprises a user terminal, the identity management system and a SP device. By utilization of the mapping relations of the plurality of the identities of the users, the identity management system can find out identity information of the users on other SP devices when the users access the other SP devices after logging in the identity management system or a certain SP device, so as to realize unified login.