To further reveal the seal mechanism of lip seals,a theoretical model was created and solved by simulation.The axial pumping effect was analyzed based on flow factor and the equation governing the flow rate was derived.Circumferential average Reynolds Equation was defined to describe the flow in the seal interface,the GW model was utilized to approximately describe the stress and the normal deformation of the contacting asperities of the lip and the shaft,and the expression of the friction transferred by fluid was given.All of the above parts was considered to be coupled and analyzed as a whole.With a lip seal used in a propeller shaft as an example,the simulation analysis was carried out based on its actual operating conditions and structural parameters to obtain the distribution of angle of asperities,film thickness and pressure,and the relationship between the net flow rate with the rotational speed and the roughness of the lip seal was also analyzed.The results that the net flow is increase with the increasing of speed,but the growth rate gradually slows down.Net flow is increased linearly with the increasing of surface roughness,but high surface roughness will result in the increase of leakage and cause the surface to be worn more easily,therefore,the selection of actual lip roughness should consider various factors synthetically.