The disclosed system includes soft exchange and access network, as well as multi media gateways connected to the access network through narrowband connection. V5 interface in soft exchange builds V5UA link to the multi media gateways respectively to carry main channel, secondary channel of V5 interface. When media gateways in main channel are in fault, V5 interface rearranges main channel to V5UA link of carrying secondary channel. The invention also discloses method of making backup for V5 interface in device level in NGN network. The invention guarantees V5 interface between soft exchange and equipment in access network in normal state in maximum extent without dependence on equipment of media gateway and equipment of access network from specific manufacturers. Thus, the invention guarantees normal users' service under V5 interface, and increases capability of disaster tolerance for V5 interface between soft exchange and equipment in access network.