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[Objective] Time synchronization is the foundation for ensuring the coordinated linkage of sub-systems within the signaling system, which directly affects the punctuality and operational safety of trains, serving as the basis for achieving train FAO (fully automatic operation). Therefore, it is necessary to study the train FAO signaling system synchronization scheme. [Method] The role of time synchronization devices in the signaling system is introduced. A time synchronization scheme is proposed and explanation is provided for the scheme. [Result & Conclusion] The proposed time synchronization scheme is as follows: the communication front-end processer of the signaling system obtains a unified time source from the clock system through the network, and time services are provided only by the host of the communication front-end processer. The application server as the host of client synchronizing with the communication front-end processer, and only the application server host is used as the server to provide time services to the lower-level devices. The gateway server and various terminal devices synchronize with the time of the application server host, with the gateway server host serving as the clock source to provide time services to the lower-level devices. The ATC (automatic train control) on-board devices and DCS (data communication sub-system) devices serve as clients to synchronize the gateway server host time. The proposed scheme utilizes different synchronization methods for the internal and external environments of the signaling system, avoiding internal signaling system jumps caused by external clock jumps, ensuring the time synchronization accuracy of the equipment. The time synchronization accuracy can reach millisecond level, thereby guaranteeing the requirements for train FAO.