The invention relates to an auxiliary hoisting device for outer-side cross arms of a crank arm of a wine glass type ultrahigh-voltage transmission line iron tower. The auxiliary hoisting device comprises a force arm, a mast, a connecting steel rope, a support device, an overturning steel rope, a fixed pendant, a fixed pulley and a support tube, wherein one end of the force arm is connected with one end of the mast, the other end of the force arm is connected with the other end of the mask through the connecting steel rope, and the force arm, the mast and the connecting steel rope form a triangular structure; one end, connected with the mast, of the force arm is hinged with the support device, the other end of the force arm is connected with the fixed pulley, and the other end of the mast is connected with the fixed pendant through the overturning steel rope; two ends of the support tube are respectively connected to the force arm and the mast; the support device and the fixed pendant are fixedly arranged on middle cross arms. The auxiliary hoisting device is fixed at tops of the outer sides of the middle cross arms for directly hoisting the outer-side cross arms in a large-angle inclination manner, so that the problem that a normal pole is difficult to hoist in position, the probabilities of injuring people and damaging machines in a hoisting process of the outer-side cross arms of the crank arm are reduced, and the integral construction efficiency of the wine glass type iron tower is increased.