Abstract: The response time test of the reactor protection system is crucial for ensuring the safety of the reactor. To address the challenges posed by measuring the response time of the Tricon platform reactor protection system, which involve multiple remote devices and long-distance transmission, this paper proposes a new communication method for response time testing. This method enables four-wire communication for measuring the response time of the Tricon platform reactor protection system by establishing a star topology suitable for devices distributed across different areas, particularly in situations where the rooms have high isolation or the devices are located at considerable distances. It uses four core wires to transmit both data and synchronization time signals, solving the problem of measuring the response time of multiple devices distributed across different areas. Furthermore, it has been successfully validated at the Fuqing Nuclear Power Plant, demonstrating the feasibility of the method.