Abstract: Studies the effect of spool figure upon the perfarmance of hot gas valves.The internal flow fields of three hot gas valves with different spools were simulated based on dynamic grid technique by the method of CFD.One user defined function was used to calculate the movement of spool.Characteristics of flow fields of those three valves was analyzed.Cold air test was carried out to validate the numerical simulation.The result of numerical simulation indicated that convex valve steadies quickly and provides higher pressure of chamber and higher mass flow rate of pneumatic component.Rectilinear and convex valves have higher temperature peak values at their inflexion.