Abstract: A flowing water hydroelectric generator is consisted of a motor attached by power cord, an overdrive gear set assembled on the motor's axial and couple fixed axles including a sun gear, several planet gears and a ring gear having a gear hole, a shaft able to be inserted through the gear hole, a housing installed on the motor able to block and seal the overdrive gear set on the motor and an impeller connected to the shaft. The generator can produce more power because of the motor's rotating speed-up driven by the overdrive gear set turned by the shaft spun by the impeller swiveled by flowing water and has a variety of installing combinations and easily be installed or removed. The best power generation efficiency can be achieved due to the generator's prolonged service life, small volume, great capacity and good transmission.