This application provides a core network control plane device selection method and apparatus. The method includes: obtaining, by a source core network control plane device, first network slice selection assistance information of a terminal device; and if the source core network control plane device cannot determine a target core network control plane device indexed by the first network slice selection assistance information, sending, by the source core network control plane device, the first network slice selection assistance information and first indication information to the terminal device, to trigger the terminal device to send a first registration request message. The first indication information indicates that a temporary identifier of the terminal device is invalid, and the first registration request message carries the first network slice selection assistance information and a permanent identifier of the terminal device.