Abstract: The computational fluid dynamics(CFD) simulation technique based on Navier-Stokes equations is used to study the local separation flow characteristics of the flaps of the HTV-2 hypersonic vehicle. The effects of different flight altitude, wall temperature and flight angle on the separation characteristics are analyzed. As the altitude increases, the adverse pressure gradient formed along the flow direction decrease, resulting in a smaller separation zone near the flaps and the surface of the aircraft. Increasing wall temperature leads to the streamwise velocity gradient upstream of the compression corner decreases, thereby increasing the separation zone. With the angle of attack increases, adverse pressure gradient increases. However, the viscous force increasing is more obvious, the flow separation is less likely to occur and the separation zone is reduced.