In order to improve hit potency of guns, this paper has researched the method of ballistic based on genetic algorithm and Runge-Kutta. Firstly advanced a ballistic model based on difference Runge-Kutta, which can accurately solved the coordinate of point of fall after gaining the information of target position. Then, put forward an algorithm of optimal angle of fire based on genetic algorithm, which decreased the search range dynamically and parameters adjusted by them. Ultimately, it calculated the optimal angle of fire. Meanwhile, proved the feasibility and validity by analyzing a case, the work has an important applied value for ballistic.