The present invention discloses a method for accessing a storage server of an IM service system and an IM service system. The method comprises: IM client sending registration request message to IM service system using first user identifier; after receiving registration request message, IM service system obtaining other user identifiers associated with the first user identifier, sending registration success response message comprising other user identifiers associated with the first user identifier to IM client; IM storage client sending login request comprising any one of multiple user identifiers to storage server; storage server receiving login request and obtaining other user identifiers associated with the user identifier in login request; the storage server passing identity verification of multiple user identifiers. The problem of repeat login of a user with multiple identifiers is effectively solved when accessing a storage server, the system access efficiency is improved and the user experience is enhanced.