Electromagnetic gun can customize appropriate projectile according to the vulnerability of individual target. For an aim velocity of projectile， different voltage， current， and dimension of rails， which formed solution space with multiple feasible ones， and the optimal solution should be found. Based on non-dominated sorting genetic algorithm-II（NSGA-Ⅱ）， taking the muzzle velocity and energy efficiency as the goal， four multi objective optimization problems are proposed， in which projectile mass， dimension of rails， capacitance， voltage and current of electric power， are involved progressively. Based on Pareto optimal solution that solved with NSGA-Ⅱ， the main influence factors were analyzed， and some useful conclusions were drawn.