Abstract: A power assembly, a power system including the power assembly and an unmanned aerial vehicle (UAV) including the power system are disclosed. The power assembly may include an engine, a transmission mechanism, an electrical generator, and a battery. The transmission mechanism may include a first drive shaft and a second drive shaft, both of which may be transmittingly connected to an output shaft of the engine. The first drive shaft may be used to drive a propulsion propeller of the UAV to rotate, and the second drive shaft may be used to drive the electrical generator to generate electricity. The electrical generator may be electrically connected to the battery to charge the battery. The battery may be used to drive rotors of the UAV to rotate.