If the missile is converted to attack another target once it has aimed at one target, the repositioning will have a very serious impact on maneuvering capability of the missile. Based on the basic principle of the firing direction change of the missile body, this paper establishes a model of missile firing direction change, presents a method to realize the change by rolling of missile body in the boost phase. The simulation results show that: 1) The model can achieve the direction change in boost phase of ballistic missile; 2) The designed simulation system has certain anti-interference capability, and rolling angle command tracking effect is fine;and 3) The missile can fly steadily.