Change of cannonballs’ moving state from ship swaying is analyzed. A model for analyzing the firing accuracy of naval gun system is build based on an available model for describing cannonballs’ flying and indicator system for evaluating firing accuracy. A method for calculating reliability of simulation is learned based on requirement in current analysis. The method considers not only the compatibility between simulation and specimens, but also the specimens’ reliability. For solving the current problem in analysis, the bayesian model considering the reliability of the simulation for estimating naval guns’ firing accuracy is built. The model achieves the aim to estimate naval guns’ firing accuracy with limited specimens and simulation effectively. Contrast test based on simulation is built to verify the availability of the reliability evaluation model and the estimation model for naval gun’s firing accuracy. Results show that the reliability evaluation model can use the test specimens to evaluate the simulation’s reliability efficiently and the Bayesian estimation can use the advantages of both the simulation and the firing specimens, and estimate the firing accuracy efficiently.