According to the characteristic that cruise missile which allows satellite communication can reserves many alternate targets' paths, the path planning method for alternate target based on Floyd algorithm was put forward. The Floyd algorithm can avoid terrain and threat by adopting the path cost function with the information of terrain height and thread; the time of path planning is reduced by considering the symmetry of waypoint graph in Floyd algorithm; the path smoothing method guarantees the feasibility of path. The path planning step of alternate target and the analysis of computational complexity were presented, and the validity of such method was proved by the simulation result.