Embodiments of the present disclosure disclose a circuit switched fallback method, a network device, and a system. The method includes: determining, by the network device, that a serving cell handover process of UE is ended; determining, by the network device, that before the serving cell handover process of the UE is ended, it has been determined that the UE needs to be moved to a second network supporting a circuit switched service; and moving, by the network device, the UE to the second network. According to the foregoing method, when CSFB triggered by a CS service initiated by UE conflicts with a serving cell handover process of the UE, the CS service of the UE can continue to be performed after completing the serving cell handover process of the UE. In this way, a success rate of establishing the CS service is increased.