The bellows expansion joint is a key component of the nuclear power plant system and pipeline control. Since nuclear power equipment has high safety requirements, the sealing, lifespan and reliability of the bellows expansion joint are required. There are strict technical requirements. The size, structure and performance of bellows expansion joints directly affect the structural dimensions and main technical indicators of the pipeline. Metal bellows expansion joints have the characteristics of high operating pressure, high operating temperature, long service life, and high reliability. The working conditions are extremely harsh. There are currently no relevant domestic design and manufacturing standards, and it is necessary to refer to relevant foreign standards and technical requirements for research and development. Due to its special, complex and harsh operating conditions, the reliability requirements of nuclear-grade bellows expansion joints are very high. Once leaked, the consequences will be catastrophic. Therefore, the bellows expansion joints for nuclear-grade valves have great impact on the design and process. , manufacturing and testing all have very high requirements. Nuclear-grade bellows expansion joints generally work in high-temperature and high-pressure environments. Affected by the development cycle and cost, it is difficult to test bellows expansion joints at room temperature and high temperature. Conventional development methods are difficult to quickly and accurately develop qualified nuclear-grade bellows expansion joints. Bellows expansion joint. Applying finite element simulation technology, the performance of metal bellows expansion joints at normal and high temperatures can be simulated and analyzed. Combining it with engineering design and testing can shorten the development cycle and greatly reduce development costs. The main performance indicators of nuclear-grade bellows expansion joints include stiffness, strength, normal temperature life and high temperature life, etc. As an elastic element, it often needs to face elastic-plastic problems of large displacement, large deformation and limited strain during the working process. To solve this problem accurately, the effects of material nonlinearity and geometric nonlinearity must be taken into account