The finite element analysis software ANSYS was used to establish the thermal structural numerical model of the concave convex pipe flange system,and the influence of the stress and temperature of each component in the system on the sealing performance of the system was analyzes.The results show that the stress of flange pipe and outer flange of bolt is relatively small,and the stress of inner flange of bolt is relatively large.Under the three conditions,pretightening,pretightening with internal pressure,and pretightening with internal pressure and temperature,the radial stress transition mode of gasket changes from large to small and then to large,and the pressure stress of gasket under the pretightening condition is the largest.The change trend of bolt axial stress is gradually increased and then decreased from bottom to top of the bolt.