A numerical model for multi-lip reciprocating slip ring combined seal was established,which includes solid mechanics analysis,fluid mechanics analysis,contact mechanics analysis and fluid-structure coupling analysis.Taking PS seal with three sealing lips as an example,the oil film thickness distribution,oil film pressure distribution,rough peak contact pressure distribution,internal and external stroke flow rate and friction force of sealing interface were obtained based on numerical model.This numerical calculation method solves the problem that boundary conditions are difficult to determine in multi-lip seal,and the boundary conditions of each sealing lip in steady state can be obtained through iterative calculation.The sealing mechanism of multi-lip PS seal was clarified,and the influence of different reciprocating speed on sealing performance was analyzed.The results show that the boundary conditions of each lip vary greatly in the internal and external stroke of multi-lip PS seal.In the external stroke,there is a certain pressure at the gap between the two lips,while in the internal stroke,the gap pressure is 0.The contact pressure of the sealing surface of the outer stroke is less than that of the inner stroke.The increase of reciprocating speed will increase the net leakage of multi-lip PS seal and decrease the friction force.