The buffeting onset angle is estimated based on the Reynolds averaged Navier-Stokes(RANS) equation and the shear stress transport (SST) turbulence model, which is according to the lift coefficient criterion, pitching moment criterion and surface limit flow criterion of flying-wing unmanned aerialvehicle (UAV). Based on the detailed structure model and aerodynamic model, the structural aerodynamic coupling solving technology is built. The aerodynamic dynamic meshes adopt the combination of the spring-based and local remeshing methods. The buffeting load responses of flying-wing UAV are calculated in the time and frequency domains, respectively. The results show that based on the CFD RANS equations, the SST turbulence model and different kinds of criterions, the rigid flying-wing UAV in low-speed high-angle condition can get reasonable buffeting onset angles. The angles predicted by the lift coefficient criterion and the pitching moment coefficient criterion are more conservative than ones predicted by the surface limit flow criterion; the surface limit flow criterion method can give the detailed wing flow and the wing flow characteristics at different angles. Compared with other aeroelastic responses, buffeting is the forced vibrations, and the response frequency is not single.