The numerical simulation model of the combined air pressure reducing valve with high pressure reducing ratio was established based on the computational fluid dynamics (CFD) method.The influences of flow field characteristics and regulating parameters on the performance were studied through simulation calculation;the response surface model of the pressure reducing ratio was established based on the sample point data obtained from numerical calculation;according to the performance model,the performance characteristics and combined regulation laws were studied.The results show that the flow field of the combined pressure reducing valve is complex,and the influence of the regulating parameters on the pressure reducing ratio shows nonlinear characteristics;the response surface model with two-stage pressure reducing ratio based on the nonlinear characteristics has high precision.It is a feasible technical way to carry out the regulation law research by using the model.