A combined control surface of a tailless airplane comprises a parallelogram-shaped embedded control surface and a parallelogram-shaped elevon. Each of the two straight edges of each of the parallelograms forming the embedded control surface and the elevon is parallel to the central axis of the body of the airplane; and each of the two inclined edges of each of the parallelograms forming the embedded control surface and the elevon is parallel to the trailing edge of a positioning wing. The embedded control surface and the elevon in the combined control surface are positioned in a same span-wise position of the wing, and the position of the embedded control surface is close to the leading edge of the wing. The trailing edge of the elevon overlaps with the trailing edge of the wing. The largest deflect angle of the embedded control surface is 90DEG, and the deflect angle of the elevon is +/-30DEG. The combine control surface can increase the lift force, and makes up the lift loss caused by the opening of the embedded control surface; and the combined control surface increases the vertical static stability of the tailless layout, so the coupling rolling torque is reduced or eliminated, the separation flow area is increased, a large resistance increment is obtained, the vertical trimming burden is mitigated, and the course control efficiency is improved.