Embodiments of the present disclosure relate to the communications field, and provide a load migration method, apparatus, and system. The method includes: determining, by a source controller, a to-be-migrated UE that needs to be migrated to a destination controller; updating, by the source controller, resource information of the to-be-migrated UE in a database server, where the updated resource information includes a correspondence between the to-be-migrated UE and the destination controller; and sending, by the source controller, an inter-domain update instruction to an external network element, where the inter-domain update instruction includes an identifier of the to-be-migrated UE and an identifier of the destination controller.