Flange, gasket and bolted connection system are important contents in the design of pressure vessels and pipelines, and are also the key parts that are prone to problems in the process of engineering design and use. Due to the engineering application needs, the non-standard pipe flange, gasket, bolt and valve connection system with a nominal diameter of 450 mm were designed, and a new gasket covered by expanded graphite and 0Cr18Ni10Ti was developed. At the same time, considering the influence of flange rotation and internal pressure on the force and deformation of flange, gasket, bolt and valve, the three-dimensional finite element technology is applied to analyze the overall stress distribution of the flange connection system in the bolt pretensioning process and the pressurization process. The results show that the stress strength of flanges, bolts, etc. meets the requirements, and the gasket stress and residual compression pressure meet the density