A method and device for detaching a user equipment (UE) are disclosed in the present invention. The UE is registered with a mobility management entity (MME) in a packet switched (PS) network and a mobile switching center (MSC) in a circuit switched (CS) network. When the UE needs to detach from the PS network, the MSC receives a Detach Request with a Detach Type indicating the detaching from the PS network only; after receiving the Detach Request, the MSC deletes the context of the PS core network entity and clears the connection between the MSC and the MME. An MME for performing UE detachment is also disclosed in the present invention. The present invention helps reduce the time delay during the subsequent handover and quickly provide users with communications services, so as to improve user's experience and meet the carriers' requirements.