The invention relates to the technical field of engines, and discloses an unmanned aerial vehicle engine. The unmanned aerial vehicle engine comprises a crankcase and at least three cylinder blocks uniformly arranged in the circumferential direction of the crankcase, the interiors of the cylinder blocks and the interior of the crankcase are in communication, a crankshaft is arranged inside the crankcase, the central axis of the crankshaft is perpendicular to the central axes of the cylinder blocks, a piston is arranged in each cylinder block, and the pistons and the crankshaft are connected through connecting rods. The multiple cylinder blocks and the pistons are arranged in the circumferential direction of the crankcase, by means of the design manner, the space is saved, and the size of the multi-cylinder engine is reduced. Each piston can singly drive the crankshaft to rotate, if one of the pistons or cylinder blocks breaks down, the other pistons will continuously work, the crankshaft is continuously driven to rotate, quick stoppage of an unmanned aerial vehicle can be avoided, and the safety and stability of the unmanned aerial vehicle are improved. Meanwhile, the multiple pistons work at the same time, the stroke of all pistons is staggered, the horsepower of the engine can be greatly increased, the fly time of the unmanned aerial vehicle is longer, and the height is high.