The 4th Generation Mobile Communication Technology (4G) Long Term Evolution (LTE) is restricted by the frequency band of 1 785 ~ 1 805 MHz private network in China. Rail transit must ensure stable minimum bandwidth requirements for dual network redundancy configuration and special services, which greatly limits the service capacity of LTE-M integrated bearing system. In view of the above problems, we propose to upgrade the 4G base station, core network and vehicle mounted Terminal Adapter Unit (TAU). and add the 5th Generation Mobile Communication Technology (5G) public network Non-Standalone (NSA) base station. Therefore, 4G private network can be used as the main network of Communication Based Train Control (CBTC) system service, and 5G network is used as the auxiliary network to carry CBTC system. The 5G base station can also be used to carry large bandwidth service of rail transit private network. Our propose solution realizes the integration of 4G private network and 5G public network to carry the large bandwidth requirements of the communication system.