Based on the mathematic model of reentry movement of ballistic missile, the method of adopting preprogram trajectory to penetrate was established and solution of the penetration trajectory using genetic algorithm was studied. The genetic algorithm model which took the angle of attack changing along with reentry time increasing as the object of coding was introduced and the simulation was continued. The simulation result shows genetic algorithm can carry out the accuracy result of reentry trajectory solution with high speed, this algorithm can make the choice for application.