Since 5G networks are expensive in terms of equipment, require large investments during construction, consume large amounts of power and have high operating costs, co-location and sharing have become a new approach to operator network development and operation. This paper first introduces the networking architecture and interoperability interface of inter-network roaming in core networks, followed by the key procedures and specifications of inter-network roaming, and then analyzes the registration procedures and terminal mobility management in roaming areas. Finally, a proposal for inter-network roaming commercialization is presented, and the correctness and feasibility of the scheme are verified through interactive experiments between home 4G and visited 5G as well as between home 5G and visited 5G.