Abstract: Nuclear vessel hydrostatic test is one of the important in-service inspection methods in nuclear power plants, to verify vessels under sustained pressure integrity and sealing. According to the installation requirements of the temporary special devices, in the design stage of vessel and pipeline of nuclear power plants, the vessel body and the pipeline layout are optimized, to reduce the personnel exposure in the in-service hydraulic test, to reduce the test duration, to lower the risk of equipment and related accessories, and to reduce the maintenance cost of nuclear power plants.