This paper studied the working process of the DIRCM system. Theoretical analysis and computation have been made for the three important courses i.e. atmospheric transmission of laser radiation, laser interfere on IR sensors, reflectance of the IR imaging guider projected by detecting laser. Then they are programmed into several simulating modules carrying out corresponding tasks. Finally they are integrated into one friendly interface simulating system. This work is very essential for the fixing of the parameters of the DIRCM system.