A type of lip seal with helix ribs was investigated by using finite element simulation software.A coupled fluidstructure model was developed,which included a solid mechanics model and threedimensional flow field model.By adjusting the thickness of oil film and lip contour,a balance between fluid pressure and contact pressure was achieved.Key parameters about lip seals such as contact width,radial force and reverse pumping rate were calculated.The validity of this theoretical model was confirmed by comparing the simulated results with the experimental results.Based on this model,the static contact characteristics and dynamic flow filed distribution under nonpressure condition and pressure condition were analyzed,which helps to reveal the mechanism of lip seal with helix ribs.This new theoretic model has high computational efficiency and accuracy within a large speed range and can be applied to the development and design of other hydrodynamic lip seals.