Provided in the present invention are a method and a system for implementing a relocation between networks, wherein the method comprises the following steps of: a source wireless access controller sending relocation request message to a target wireless access controller through an Iur-g interface, wherein the relocation request message carries capability of a user equipment (UE) as well as an port number of the Iur-g interface for bearing user plane data which is assigned to the UE by the source wireless access controller; after receiving the request message, the target wireless access controller assigning wireless resources to the UE, checking that the port number of user plane corresponding to the Iur-g interface is available, and sending relocation request acknowledge message to the source wireless access controller; after receiving the relocation request acknowledge message, the source wireless access controller informing the UE to relocate.