In the original design of a second-generation nuclear power plant (NPP), when the isolation signal of the main feedwater supply is generated, the corresponding relay will be triggered to close the corresponding main feedwater regulating valve. According to the original design of the NPP, any spurious operation of the relay will cut off the feedwater supply, and then cause the reactor trip, so the four relays controlling the main feedwater regulating valves are single point failure (SPV) equipment. In this paper, desensitization of these SPV equipment is studied, and the optimization scheme of changing relay control logic to avoid unplanned reactor trip due to a single fault is evaluated. The influence of the original control logic and the optimized control logic on the spurious operation and demand failure of the regulating valves and the influence on the core damage frequency (CDF) of the NPP is compared and analyzed. The results show that under the premise of ensuring the safety of nuclear power plant, the optimal scheme can realize relay desensitization and reduce the reactor trip frequency caused by relay spurious operation.