Abstract: The design and arrangement of the recirculation valve in the main water supply system of a nuclear power plant is studied, to explore the causes for the sudden jump of the recirculation pipeline at the moment of starting the pump and accompanied by the blasting sound. The results show that the multi-stage cage regulating valve cannot be arranged in the high-pressure water supply pipeline with residual air, otherwise the destructive water hammer will be induced during the start-up stage. By optimizing the design layout of the recirculation valve, the problem of abnormal startup of the main water supply system was finally solved.