Embodiments of the present invention disclose a method and an apparatus for sharing a core network, where the method includes: first, determining, by a mobility management network element, that a user equipment does not support network sharing; and then, sending, by the mobility management network element, a location update request message to a mobile switching center or visitor location register MSC/VLR, where the location update request message includes indication information that the user equipment does not support network sharing, or the location update request message includes a location area identity LAI including a common public land mobile network identifier common PLMN ID, or the location update request message includes an LAI including a common PLMN ID and includes a circuit switched domain public land mobile network identifier CS domain PLMN ID. The present invention is applicable to the field of communications systems.