In order to improve the accuracy and the combat efficiency, firing errors and firing observation were analyzed based on the principle when ship borne gun fired one dimension trajectory correction projectile. Firing errors were classified into forecasting errors and correcting errors, and the new firing correction method was demonstrated with the deviation between detecting point of fall and target or predicted point step by step. Firstly, the part correcting errors were corrected. Secondly, the forecasting errors and the residual correcting errors were corrected. It is proved that the new firing correction method can improve firing accuracy by simulating 10 000 times with Monte-Carlo method taking certain type one dimension trajectory correction projectile as example.