The invention discloses an outer rotor engine and an unmanned aerial vehicle. The outer rotor engine comprises a fixed eccentric shaft fixed on an engine base and serving as an inner support of the outer rotor engine and an outer rotor mechanism sleeved outside the fixed eccentric shaft and rotating to work, wherein the fixed eccentric shaft supports the outer rotor mechanism via a bearing, and the outer rotor mechanism comprises a pentagonal inner rotor and an outer casing rotor; an inner gear ring on the inner surface of the pentagonal inner rotor is engaged on an outer gear in the middle of a cylinder cover of the outer casing rotor, the position difference between the inner gear ring and the outer gear is a gear center distance, and the gear center distance is guaranteed by the eccentricity of the fixed eccentric shaft; the pentagonal inner rotor is eccentrically arranged in the cavity of the outer casing rotor, and carries out generating motion in the cavity of the outer casing rotor; the outer casing rotor rotates to drive the pentagonal inner rotor to rotate, and the rotating directions of the pentagonal inner rotor and the outer casing rotor are same and located on the same fixed eccentric shaft. The outer rotor engine can obtain cooled air flow, does not need balance weight, and is advantageous on heat dissipation.