Designing the pneumatic DTH by the method of anology, experience and actual test, the investment is large, the cycle is long, and it is difficult to achieve the optimization. In order to research profoundly the DTH work mechanism and describe piston movement laws in detail, physical model is established according to the actual conditions, finite difference method is adopted, thermodynamics and kinematics are applied. Using object-oriented programming, the pneumatic DTH computerized simulation software is developed whose integrated development environment is VB. The software can calculate acceleration, velocity, displacement, pressure, temperature of the front and back air chamber at any time and the operating performance parameters of the pneumatic DTH. The law of many factors influencing on the pneumatic DTH performance can be found and the optimization of the pneumatic DTH structure parameter can be achieved by the ergodic method. Not only the pneumatic DTH but also the no-dig impactor is designed by computerized simulation.