Provided is a method for unfolding primary lead ropes of a transmission line by a remotely-controlled unmanned aerial vehicle (UAV). The method comprises the following steps: a lead rope fixing device is installed at the bottom of a UAV; four primary lead rope unfolding racks respectively wound with a primary lead rope are arranged on the ground at the starting position of a wiring section in a line, and the heads of the ropes are fixed to the lead rope fixing device of the UAV; and the remotely-controlled UAV is started to fly to above a first-base tower, and an overhead operator on the tower gets hold of the four primary lead ropes and places the four primary lead ropes in a specified rope buckle, thus completing single-base tower operation. Under the control of a ground operator, the remotely-controlled UAV continues flying to a next-base tower. The steps are repeated. The remotely-controlled UAV sequentially passes by all towers in the wiring section. Finally, the remotely-controlled UAV lands at a specified place, and the primary lead ropes are removed. The method of the invention has the beneficial effect that the risk of high-altitude flying can be avoided for paramotor pilots. The four primary lead ropes are dragged at the same time, which reduces the labor intensity and workload of operators and improves the work efficiency.