Embodiments of the present invention disclose a method for implementing a One Card Multiple-Number (OCMN) service, which includes: establishing a mapping relation between an internal network number of a user and at least one external number of the user; determining an internal network number of a called user corresponding to an external number of the called user according to the mapping relation when a calling user initiates a call to the external number of the called user; connecting the call to the called user according to the internal network number of the called user. Embodiments of the present invention further disclose a system. According to the embodiments of the present invention, the OCMN service may be implemented flexibly.