The invention relates to a brushless DC (Direct Current) motor for unmanned air vehicles, belonging to the technical field of unmanned air vehicle powerplants. The brushless DC motor comprises an external rotor composed of a rotor end cover, a rotor yoke and a permanent magnet, a stator composed of a winding, a stator iron core and a stator yoke, an upper bearing, a lower bearing, a rotation shaft and a stopper ring, wherein the outer diameter of the rotor yoke is the same as that of the rotor end cover, the rotor yoke is fixed at the lower end of the rotor end cover, the permanent magnet is fixed on the inner wall of the rotor yoke, and the number of magnetic poles of the permanent magnet is 24; the stator iron core comprises 18 slots, the stator yoke is sleeved on the inner wall of the stator iron core, and the winding is coiled on the outside of the stator iron core; the upper bearing and the lower bearing are respectively fixed on two ends of the rotation shaft; the stator is connected with the rotor through the rotation shaft, the stator is embedded inside the rotor end cover, and the stopper ring is sleeved on the rotation shaft. In the invention, by directly driving airscrews, the brushless DC motor is beneficial to elimination of efficiency loss of a driving system, and improvement of lift force/power consumption ratio and lift force/mass ratio of air vehicles.