According to the characteristics of controllable muzzle velocity of the new shipboard gun, a method for calculating the firing data based on maximum hitting probability is proposed.The projectile muzzle velocity is added as a new firing data element of the shipboard gun with controllable muzzle velocity.When striking the sea target within visual range, there is a nonlinear relationship between the hitting probability and projectile muzzle velocity.The model of projectile exterior ballistic trajectory and the equation for solving hit problem are established for calculating the trajectory.Based on the concept of golden section, the projectile muzzle velocity is obtained through dichotomy.Constrained by the condition of maximum hitting probability, the method can calculate the firing data of the new-energy shipboard gun weapon effectively.