Embodiments of the present invention disclose a method and a system for CS core network evolution, and a network device. The evolution method includes: EMSC connects with an IMS network and serves as a TAS in the IMS network to provide a voice service for a user in the IMS network, where the EMSC is obtained by upgrading a Mobile Switching Center Server in a CS core network and possesses functions of the TAS in the IMS network; and performing, by the EMSC, service processing on a service request for an existing service, and sending a service request for a new service to a corresponding application server in the IMS network for processing, wherein the service request for an existing service and the service request for a new service are initiated by a CS user who has subscribed to a new service.