Taking the piston rings and cylinder liners as research subjects,the effect of the lubricating oils of different specifications on the piston oil film thickness and friction loss was simulated by AVL EXCITE.The experimental results indicate the oil film thickness of the third piston ring of the engine has the biggest influence on the friction loss of the engine.The oil film thickness of third piston ring and total friction loss when lubricated by different lubricating oils were simulated.The results indicate that when the engine speed is from 1 000 r/min to 3 000 r/min,the piston ring is in a state of mixed lubrication,and the oil film thickness is firstly increased and then decreased with the increasing of engine speed.It is helpful to reduce the friction loss by reducing the viscosity of lubricating oils at low engine speed,but low viscosity will make the thickness of piston oil film become thinner in the heavy load and result in the increase of friction loss of engine.The simulation results wre verified by the NEDC test results of vehicle.