The positioning errors of three common guiding ways (radar, head-up display and aiming-pod) of laser-guided bomb releasing when immediate attack were analyzed, and the simplified error models were established; The effect of the principles and errors of fire control system on target acquisition probability of laser-guided bomb were studied. Finally, a modified firing table method which can effectively amend the effect was given. The simulations show that the modified method not only has a high reliable and wide application in engineering, but also can improve target acquisition probability markedly.