The invention relates to a rotating machine, in particular to a buoyant energy power unit which rotates by taking advantage of buoyancy. The buoyant energy power unit comprises a water tank part, a rotating shaft part and a transmission case and is characterized in that the rotating shaft part comprises a rotating shaft and an inflator wheel arranged on the rotating shaft; the rotating shaft is arranged above a water tank; the inflator wheel consists of an inner strand and an outer strand; the center of the inner strand is provided with a fixing hole for connecting the rotating shaft; the inflator wheel is filled with air; 1/4-1/2 of the inflator wheel is positioned in the water tank; the water tank part comprises the water tank, a water tank cover and a booster pump; lateral surfaces of the water tank and the water tank cover are provided with hole grooves which can pass through the inflator wheel; water seals are arranged peripherally around the hole grooves; the booster pump pressurizes the inside of the water tank; the rotating shaft is connected with an input shaft of the transmission case; and an output shaft of the transmission case is a power output shaft. The buoyant energy power unit can solve the present problems of energy crisis and energy scarcity and replace a traditional internal-combustion engine, motors and other power units and is most suitable for a relatively stable working environment such as a power station and the mine exploration.