In order to solve the problems of the Stirling machine piston rod working medium leakage,the structure of cap seal was improved,and the two-dimensional axisymmetric model of the sealing structures was established by using finite element analysis software ANSYS.Based on the actual operation condition,the performance of the improved sealing structures were analyzed.By changing the boundary conditions,the influence of working medium pressure,friction coefficient and piston rod speed on the performance of improved sealing structure was investigated.The results show that the improved sealing structure eliminates the stress concentration problem of the original O-ring structure,and the maximum contact stress is increased.The effective sealing area of the improved sealing structure is increased by 40%,and the maximum stress of O-ring is reduced by nearly 50%.Among the three key parameters,the medium pressure has the greatest influence on the sealing performance.For the improved sealing structure,the sealing performance is the best when the medium pressure is from 6 MPa to 8.5 MPa.