An inter-network interworking method, an apparatus, and a system are provided, and relate to the field of communication technologies, to ensure that a service is not interrupted when a terminal moves from a second network to a third network. The method includes: When the terminal supports a NAS capability of the third network and/or a network name corresponding to the terminal supports interworking between the second network and the third network, a second access management network element sends a session management request including a session identifier to a first session management network element that supports interworking of the terminal among a first network, the second network, and the third network. The second access management network element receives, from the first session management network element, a session management response including a session context of the terminal in the third network. According to the method, the session context of the terminal in the third network can be prepared in advance when the terminal accesses the second network, so that it is ensured that the service is not interrupted when the terminal subsequently moves from the second network to the third network.