The utility model discloses a range extender assembly and an electric vehicle thereof, the range extender assembly comprises an engine, a generator and a rotating speed detection device for detectingthe rotating speed of a crankshaft of the engine, and the generator and the rotating speed detection device are respectively arranged at two ends of the crankshaft of the engine; the rotating speed detection device is far away from the generator, so that electromagnetic interference of motor power generation on rotating speed signal acquisition can be prevented, and rotating speed signals can be accurately detected.