The probability of our aircrafts being shot down is modeled to improve the safety of penetration flight, and to promote the probability of running task successfully. By improved genetic algorithm, with the probability of being shot down as the fitness function, and the distance between an individual and solution space as punishment function, the best plan can be found. Constrained optimal save strategy is being used to prevent the solution from early convergence. Variable arithmetic hybrid operator can limit the individual in solution space. As the result, after 150 times performance, the best flight can be gotten as O（120，550），A（226.2，495.7），B（345.8，364.3），T（330，180）, whose probability of being shot down is 0.0193.