The CFD method is employed to simulate numerically the steady and unsteady hydraulic characteristics of an ATS control valve. The steady simulations provide the three dimensional distribution of the flow field and the hydraulic characteristic curves of flow rate and pressure drop under various openings. The comparison between the calculated and experimental results shows good coincidence. The unsteady change during the opening and closing process of the valve are simulated numerically. The curves of the flow rate and the axial force exerting on the valve cone by the fluid changing with the time are given and the analysis of the influence of the opening and closing velocities is carried out.