Abstract: In order to study the separation press of the cylindrical paltes launched form the surface type IR decoy such as MJU-B50 armed in U.S. air force, the method solving three-dimensional compressible RANS equations described by ALE finite volume method coupled with the rigid motion equations was established, and the collision detection and the collision response model were developed to solve the collision between the plates. The three-dimensional unsteady initial separation process of the several plates was numerical simulated at Mach number of 0.8. Research shows that the plates collide frequently at incipient motion under close initial locations, cause the inconsistent motion and accelerate the separation course. The separation order of the plates group is mainly affected by the aerodynamics of multi-plates interference, the plates separate in a fixed law and the verified order separation characteristics existed in the dynamic test of plates dispersal.