The invention discloses a rail transit line changing transferring method and system. Each line is configured with an APN in advance. When an account is opened for TAU equipment, the APN capable of being accessed to the TAU equipment is determined according to the line distributed for the TAU equipment, meanwhile, each APN capable of being accessed is configured with a corresponding static IP address, and the different APNs capable of being accessed are configured in the TAU equipment to correspond to different target address network segments. In the operation process of a train, the TAU equipment judges whether PDN connection of a new line needs to be built or not according the mapping relationships between a received data package and the target address network segments as well as between the saved APN and the target address network segments, if yes, triggering is conducted to built connection with a corresponding target PDN, and when a service PGW of the TAU equipment detects the situation that the condition of disconnecting with the source PDN is met currently, the TAU equipment is disconnected with the source PDN. By adopting the rail transit line changing transferring method and system, signal system transferring at the time of line crossing operation of the train can be achieved.