Abstract: The low-aspect-ratio flying-wing configuration was designed as a common research model in China, wind tunnel test results show lift force experience a sudden decrease at M=0.9 as the angle of attack between 12° and 16°, numerical methods are also used to investigate this behavior in detail. The generation, development, and breakdown of vortex are all concerned. Results show that the flying-wing generates vortex lift at α=4°, Shock/vortex interaction is responsible at transonic speed, as the angle of attack increases. As long as the shock is strong enough to break the balance between shock and vortex, vortex breakdown would occur and new balance mechanism would set up.