Abstract: On the condition of full lubrication test , Coupling Euler Lagrange ( CEL ) method was introduced to solve the extrusion process of lubricating oil between cylinder and piston with micro pits Kinetics equation of lubricating oil was described with Navier -Stokes ( N -S ) equation in Euler coordinate system. Isotropic linear elastic equation in Lagrange coordinate system solved the piston -cylinder system Penalty function method was adopted to transfer the physical parameters of solid to the fluid element , thus fluid -solid coupling was implemented directly The presented results indicated that free surface of lubricating oil was better traced by CEL method The piston skirt with micro pits extruded lubricating oil into pits .However , smooth piston skirt extruded lubricating oil out of the gap and can not store the lubricating oil Contact stresses increased during the extrusion process , especially on the surface of smooth piston skirt Load bearing ratio of lubricating oil stored in micro pits reached 0.3 Therefore , oil film in micro pits had certain load -bearing ability The numerical results were in good agreement with experimental results