In order to study the dynamic sealing performance of the oilfree lubrication cap type seal of Stirling engine piston rod,the twodimensional axisymmetric finite element model of the cap seal was established by using the finite element analysis software Abaqus.The effect of working fluid pressure the sealing performance of cap seal was studied based on the actual working conditions of the system,and the effective sealing area at different pressures was obtained.The result of static sealing performance analysis shows that the contact stress between the cap seal ring and the piston rod is the key to the seal.The result of dynamic sealing performance analysis shows that the contact stress and seal area are increased with the increasing of working fluid pressure,and the contact stress at outer stroke is slightly larger than that at the inner stroke.The effect of ambient temperature,friction coefficient and reciprocating speed of piston rod on the dynamic sealing performance of cap seal was analyzed through the dynamic simulation of thermal coupling.It is found that the ambient temperature has little effect on the temperature field of cap seal,and the heat source mainly comes from frictional heat.The reciprocating speed has little effect on the sealing performance of cap seal,while the friction coefficient has a larger effect on the sealing performance.The smaller the friction coefficient,the better the sealing effect and the longer the service life of the cap seal.