Research and design to the characteristics and performance parameters of the hydraulic impactor with a nitrogen chamber have been done. The speed-time objective function of piston's motion of the hydraulic impactor was constructed, the nonlinear mathematical model of the piston's returning motion，shocking motion based on the nitrogen chamber was established, and the differential equation of the piston movement curve was gotten. Through determining some of parameters of objective performance, thereby the performance parameters of the rest were deduced. By the design method about parameters, the performance parameters to the movement parameters of the machine could be linked, which facilitated the determination of structure parameters. This method has reference value to the practical application and theory research.