For the longitudinal landing control problem of flying-wing UAV with unknown external disturbances, a backstepping L₂ gain robust control scheme based on super twisting sliding mode disturbance observer and tracking differentiator is proposed. The tracking differentiator is introduced to calculate the derivative of virtual control law which is very difficult to evaluate with the traditional backstepping control. Super twisting sliding mode disturbance observer and L₂ gain robust item are designed to increase the robustness of the control system. Simulation results show:the altitude and airspeed of UAV are tracked on control command, vertical ground speed is within the allowable range. Compared with traditional PID control scheme, the proposed control scheme has better automatical landing control performance.