In this paper,by specifying motion parameters,a numerical method is developed to simulate entire sabot motion process from launch to exit muzzle blast,which solves 2D axial symmetry unsteady N-S equations with equal displacement variable time step size and moving chimera grid technology.The numerical launch process of a high velocity projectile is accomplished,and the detailed instantaneous unsteady flow and sabot separating force variation curve are obtained.The change rule of sabot separating force is analyzed,and the reason for the second peak value in separating force vs.time or displacement variation curve is confirmed.Finally,there are some proposals on the threshold of sabot separating force in engineering design.