Abstract: The working performance of the hydraulic percussion impactor is one of the main factors which affect its working effect in practice. According to the operating characteristic of the fluidics and the theory of hydromechanics, a dynamic model of the impactor is established, in order to bring the percussive rotary drilling technology into full play. Also a simulation program is developed to calculate the working properties of the impactor. By using the simulation program, the variation laws of the basic parameters of the hydraulic impactor under different structural parameters and hydraulics are obtained. The dynamic model can not only help to improve the design of the impactor, but also help to determine its working properties and design the percussion drilling bottom hole assembly. The research results have been applied to Longhui 4 well and Tiandong 90 well in eastern Sichuan, playing an important role in guiding the field working design.