The main seal of the aviation actuator is a reciprocating seal,which plays an important role when the aircraft adjusts its attitude.Taking step seal commonly used in aviation actuator as an example,the friction and reverse pumping rate as seal evaluation indicators,the reciprocating seal mixed lubrication model was established by solving the Reynolds equation with EHL and IHL methods,and the calculation method of the friction and reverse pumping rate of the reciprocating seal system was deduced.According to the theoretical analysis,the surface topography parameters of the sealing lip and the angle between the lip and the piston rod were analyzed by structural parameterization.The results show that the selected surface root mean square roughness,lip and piston rod inclination angle are all satisfying that the reverse pumping rate is greater than zero.The friction force is proportional to the surface root mean square roughness and the oil inclination,and inversely proportional to the air side inclination.The optimal structural parameters of the seal lip are obtained through analysis,which provides a reference for the structural optimization of the reciprocating seal rings.