Flow coefficient is an important indicator of engine performance, this study is how to improve the flow coefficient of the intake and exhaust valve, improve the flow coefficient will increase volumetric efficiency. In the natural intake engine, try to reach 100% volumetric efficiency is the challenge, because the volumetric efficiency represents the engine torque, so the flow coefficient is very important on the engine parameters.Using Gambit to crate intake model and export model, CFD software calculate the result and analysis, decrease the numerical valve error from simulation to experiment. Transform the valve geometry to increase flow coefficient.