The invention belongs to the technical field of unmanned aerial vehicles, in particular to an automatic retracting and retracting folding part of an arm of an unmanned aerial vehicle., the part comprises two parallel mounts, A fixture is attached to the UAV body, the fixing base is provided with parallel, Horizontal guide chute, Bolt slide rods are arrange in that two guide chutes, the two fixtures are connected by a connecting rod with a threaded hole on the rear side of the guide chute of the two parallel fixtures, by taking a hole as the central position, a screw rod is vertically connected on the bolt sliding rod, the screw rod is connected with a motor after passing through the hole of the connecting rod, a connecting seat of the arm rod is arranged to be connected with the fixing seat through a rotating shaft, two extension arms are arranged at the front end of the connecting seat, and the extension arms are contacted with the lower part of the bolt sliding rod. The invention can realize the automatic retracting and releasing of the arm of the unmanned aerial vehicle (UAV) and enlarge the flight field of the UAV.