In order to research the impact motion law of the dual-fluid rotary valve impactor in rotary percussive drilling， and optimize its performance parameters， through the analysis of its forces in the phases of stroke and return， the finite difference method is used to create the mathematical model of the rotary valve piston movement， and a simulation computer program compiled with MATLAB software is applied to simulation of the dynamic process of the rotary valve piston to obtain the optimal impact performance parameters of the dual-fluid powered rotary valve drilling impactor. At the same time， the influence of the difference in the area between the upper and lower chambers of the impactor， and the flow rate and pressure drop of the oil pressure system on the impact performance of the dual-fluid powered rotary valve drilling impactor is studied， and the orthogonal analysis test for impact energy， impact frequency and impact power is designed. The results are optimized by Design-Expert software to improve the working performance of the impactor. The results show that the piston rod diameter and pressure drop have prominent effects on the impactor performance， while the flow rate has little effect on the impactor performance. After optimization， the impact energy， impact frequency and impact power are increased by 21.88%，12.9% and 37.6% respectively. The research has guiding significance to the design and application of hydraulic impactors.