Abstract: For rapid-fire guns, the stationary normal shooting error sequence was decomposed as common and uncommon components; furthermore, the common component was decomposed as prediction value and prediction error. Based on the above decomposition, the expression of mean damage probability was proposed for the shooting process in certain initial values with strong and weak correlation errors; then the expression of damage probability of the weapon systems was given for uncertain initial values. Compared to the current damage probability calculation models including those listed in the national military standards, the model given is more accurate.