A load migration method, apparatus, and system. The method includes obtaining, by a first controller, in a process of migrating a user equipment (UE) to the first controller from a second controller, a first temporary user identifier of the UE, the first temporary user identifier comprising a second identifier of the second controller, allocating, by the first controller, a second temporary user identifier to the UE, the second temporary user identifier comprising a first identifier of the first controller, transmitting, by the first controller, the second temporary user identifier to a database server for updating the first temporary user identifier by the second temporary user identifier, and sending, by the first controller to an external network element, the first identifier of the first controller.