The invention relates to a brake device of an unmanned aerial vehicle rotor wing. The brake device comprises a drive shaft, a concentric drive gear, a brake disc A, a driven shaft, a concentric driven gear and a brake disc B. The concentric drive gear is fixedly connected to the output end of the drive shaft, the brake disc A is arranged on the drive shaft, the concentric driven gear is fixedly connected to the input end of the driven shaft, and the brake disc B is arranged on the driven shaft. The rotor wing comprises a rotor wing head and a main shaft, and a concentric main shaft gear is arranged on the main shaft. A brake component A is arranged on the brake disc A of the brake device, and a brake component B is arranged on the brake disc B. The drive gear and the driven gear are symmetrically arranged in a concentric mode, the main shaft gear is respectively meshed with the drive gear and the driven gear, and the main shaft gear, the drive gear and the driven gear are spiral beveled gears. In the prior art, when the main shaft gear brakes for deceleration, abrasion, caused by relative torsion and stress concentration, to the main shaft gear is reduced, and stability is improved when the rotor wing decelerates for transmission.