According to the environmental conditions and requirements of high temperature and high pressure heat exchanger,a self-tightening seal structure was designed to overcome the deficiency of common hydrostatic seal forms.The sealing structure can ensure a reasonable gap at room temperature,when working in hot state,the sealing structure can realize the self-tightening by thermal expansion according to the characteristic that different materials have different coefficient of thermal expansion,so as to achieve good sealing effect.The selection of sealing material,the tolerance and clearance of the seal structure were analyzed theoretically.The rationality of seal structure was verified through the thermal expansion analysis,stress analysis and fatigue analysis by finite element software.The sealing performance test was carried out for the self-tightening seal structure.Test results show that sealing structure can achieve selftightening by thermal expansion,and the sealing performance can meet the requirements of usage.