The flow field in a moving cartridge poppet valve is simulated and analysed with CFD technique. The 3-D geometric model of the valve is established by using software Pro/E according to the practical parameters and structure of the standard cartridge poppet valve. The mesh of the model is generated and fractionized by the preprocessor Gambit. When valve is under moving state, the simulation is carried out with dynamic mesh method, the moving speed is giving by using self defined function UDF. The relationship between transient flow force acting on the valve cone and the discharge coefficient to the flow and valve displacement during closing and opening of valves are obtained.