Abstract: Based on the EHL theory, the average flow model and the asperity contact theory, both the finite difference method(FDM)and the multi-body dynamic (MBD) method were used synthetically with component mode to analyze the movement and lubrication characteristics of the floating piston pin for diesel engine. And the effect of the surface roughness on the friction power loss of piston pin bearing was also analyzed. The results show that, the angular velocity of piston pin is small, which is almost zero in the entire power stroke; the piston pin bearing works under mixed lubrication condition in most time, and works under fluid lubrication condition only when the connecting rod's revolving angle is in maximum at the intake stroke and exhaust stroke. Through appropriately decreasing the surface roughness of piston pin (hole), the angular velocity of piston pin can be increased in the power stroke, and the total friction of piston pin bearing can be reduced significantly, which will improve the lubrication condition of piston pin.