Oil consumption of one certain diesel engine has been reduced by optimizing piston structure and piston kids clearance. The oil consumption principle inside the liner of engine was analyzed. Engine test was applied to validate the effect of the optimization. Due to the analysis, enlarge the pressure grads between piston top land and the 2nd land can push the 1st ring to the groove downside steadily. Adding or enlarging oil containing pocket above and below oil ring groove can reduce the oil pressure in these areas. Reasonable and large clearance between piston top land and cylinder liner help the gas burn completely.