The structure of a new negativepressure suction valve was designed and optimized by using the principle of fluid mechanics and the software of FLUENT, and the mechanism of negativepressure was described. The results show that the smaller distance between valves inlet and contractions outlet of the designed valve, the greater the pressure generated of vacuum suction, but the flow has heavy turbulence in the internal flow field, and the compressed air will flow back into the adsorption chamber. It is recommended that the distance between the inlet and the contractions outlet is suitable to set about 5/8 times of the air chambers axial length. At the same time, the smaller of angle between the contractions outlet and the axis of the valve, but the flow resistance is also increased accordingly, and more difficult to process, so the recommended value of the angle is 30°.