The pressure vibration failure of the large flux pressure reducing valve (PRV) was analyzed. A dynamic mathematical model of the PRV system was developed to simulate this failure, and a simple and effective method of reducing the area of the control cavity inlet to enhance the stability of the pressure output response of the PRV was found by the simulation and validated by the experiments. The result of the simulation shows that the vibration problems of the large flux PRV are related not only to the design parameters of the PRV, but also to the backward tubes connecting to the PRV.