4.Down Hole Service Company Sinopec Zhongyuan Petroleum Engineering Ltd, puyang Henan, 457164, China)#$NL：Aiming at the problem of piston failure of down-the-hole (DTH) hammer, based on the working principle of the DTH hammer, the mathematical relationship between the mathematical model of piston motion and the structural parameters of piston was established by using the law of conservation of energy, ideal gas state, and steady flow energy equation. Taking the calculated piston motion velocity as one of the boundary conditions, the finite element method is used to further analyze the piston dynamic response in the process of piston bit percussion. Moreover, the position of the maximum stress of piston coincides with the on-site piston fracture position. In this paper, the effects of different piston front surface lengths, piston front diameters, and piston center bore diameters on the impactor performance parameters were studied. When the diameter of piston front face increases, the impact energy decreases linearly and the stress amplitude of piston decreases. When the length of piston front face increases, the impact energy decreases and the stress amplitude of piston decreases. When the diameter of the front face of piston decreases, the impact energy decreases and the piston stress decreases linearly. Based on the above analysis results, the original structure of the piston was optimized, and the stress of the optimized piston was reduced by 10.2% compared with the original model.