Abstract: In the separation process of long-range-launched UAV, the attitude change and trajectory directly affect the safety and stability of the parent aircraft. In this paper, based on overset grids, a fluid and rigid body motion coupling method was proposed to simulate the dynamic separation process of UAV. WPFS standard model was used for validation. It is found that the simulation results are in good agreement with the experimental data, and the numerical simulation method is effectively verified. The simulation of UAV separation process was realized by using the proposed numerical simulation method, and the change of UAV's position and attitude with time in the process of separation was obtained. Based on the simulation results, an optimal design of UAV launching scheme was proposed.