The utility model relates to a power gearing of a small power machine, which is provided with an overrunning clutch, a centrifugal clutch, a speed reducer with less tooth difference, a controllable flywheel of a two-way claw type and shifting assemblies, wherein each assembly is fully concentric with a crank shaft of an engine, the overrunning clutch and the centrifugal clutch are axially overlapped, and the controllable flywheel, the shifting assemblies and the speed reducer with less tooth difference are axially overlapped and are provided with common elements and reasonable connection. A bearing is a high-speed element, a gear is a low-speed element, and the original shaft output is changed into the wheel output. Through adopting the structure, the utility model greatly shortens axial dimension, has the advantages of no noise, long service life and convenient operation, is suitable for various bicycles and small agricultural machines, and is an ideal power gearing.