High aspect-ratio flying wing configurations usually use split-drag-rudder (SDR) and a set of elevons to fulfill the lateral-directional control, without the traditional vertical tail and rudder. The control characteristics of SDR were specially researched, including the generation of the roll and yaw control moments and the control power effects, compared with the conventional side-force-rudder. The ability and characteristics of the yaw and roll control of high aspect-ratio flying wing configurations were presented, including lateral-directional control trimming and maneuver coordination. And the differences between the conventional aircraft configurations and flying wing configurations were emphatically analyzed. Evaluation data show that single-engine-out is the most critical case for directional control and the yaw control effect requirement is beyond what SDR can provide. As a result, the control volume of SDR ought to be properly increased or the current flying wing configuration needs improving.