Abstract: The working principles of the reverse counterboring pneumatic impactor were analyzed. The mathematical model of piston movement was built based on Newton’s laws of motion， energy conservation law of thermodynamics， steady flow energy equation and wave theory to explore the relationship between the performance parameters (i.e.， impact energy and rock breaking effective power) and inner piston structure parameters of the impactor. The mathematical software Matlab was used to solve the mathematical model of the reverse counterboring pneumatic impactor’s piston movement. The inner piston structure parameters which affect the impact performance were analyzed in detail to obtainthe relationship between the impact performance and the inner piston structure parameters. It was found that the drill’s impact energy and rock breaking effective power will reduce with the increase of the inner piston’s outside diameter， the inner piston’s length and the distance from the inner piston’s front face to the drill.

Key words: reverse counterboring pneumatic impactor, inner piston, mathematical model, structure parameter, performance