Method and system for accessing core network and triggering detachment from network side

The invention discloses a method for accessing a core network and triggering detachment from a network side. The method comprises the following steps of: in the processing of accessing the core network, after receiving an expandable authentication protocol (EAP) authentication success message by a rusted non-3rd generation partnership project (3GPP) access network (TNAN) network element, sending a session establishing request to the core network, wherein the session establishing request carriers an instruction of not distributing an internet protocol (IP) address; after returning the session establishing request, sending an IP address request message by user equipment (UE), requiring the IP address from the core network, and finishing the operation of accessing the core network; in the process of detaching, after receiving a detaching instruction by the TNAN network element, or depending on a local management configuration, sending a deleting session to the core network, and triggering dynamic host configuration protocol (DHCP) mandatory renewal to the UE by the core network; and requiring the IP address from the core network by the UE once again, and returning a negative acknowledge by the core network. Furthermore, the invention discloses a corresponding system which can trigger the access without adding a message and can guarantee a good compatibility with the existing network protocol; and the process of triggering the detachment from the network side is standardized.