Cluster bomb projection is a typical multi-body aerodynamic problem with relative motions, and is also a valuable application area for the overset grid method. The MI-GRID overset software, the fluid dynamic governing equation and the rigid body movement equations were employed to investigate the aerodynamic trajectory and movement characteristics in bomb separation process. The orthogonal experimental design was also employed to discuss even to assess the effect of the initial and aerodynamic interference on bomb separation movement. Results indicate that the bomb in projection flow field is greatly affected gesture motions by the shock interference. When a singular bomb is projected, the shock of the missile makes the pitching movement of the bomb vary abruptly. While the multiple bombs are projected, the reflection shock that is extracted by the bomb makes the bomb rise, which can affect the bomb bay's flowing.