This disclosure provides an attachment method and system for ID-Loc-Split in an NGN, to implement an attachment process for an IPSPLIT-based ID-Loc-Split in an NGN, which can be combined well with various existing functional entities in the NGN, wherein a user identification is represented by a Host ID, and during the attachment process, a user is located through the Host ID, and during an authentication process, a key authentication method is provided to the Host ID; when location of the user changes due to its mobility or multihoming, the Host ID does not change; the application and connection of the transport layer is bound to the user identification, such that the application and connection will not be interrupted, and an ongoing communication session and service will not be interrupted, which guarantees the security of attachment and seamless handover when the location of a host changes due to its mobility or multihoming.