The application of computer aided simulation to investigate the efficiency of an artillery air defense system, with automatic fire control system, is discussed. Deterministic and stochastic processes in a fire control system, significantly influencing the firing, are analyzed. The simulation procedure, involving the processes that precede firing (the flight of the target, motion of the aiming sight, target position measurement, estimation of parameters of target motion, ballistic calculus, gun positioning) and firing itself (the flight and impact of the projectile on the target), is proposed. The example of the computer aided simulation of firing is given.