A hydraulic power generating system designed to minimize equipment costs by simplifying the configuration thereof, to maximize efficiency of power generation by reducing loss in hydraulic power, and to allow economical and convenient maintenance of the system. The system comprises a power generator, a buoy floating the power generator on the surface of the water, and a fixing apparatus restricting movement of the buoy and the power generator. The power generator comprises a looped rail, a plurality of pulleys moving along the rail, a coupler to join the plurality of pulleys, a plurality of wings, each being installed to each of the pulleys to move the pulley by absorbing flow energy of water, and a generator installed in the rail to generate electricity after receiving kinetic energy of the pulleys through power transmission gears. The system is enhanced in its configuration, allowing economical and convenient maintenance of the hydraulic power generating system, while not being restricted as to the location where the power generator may be installed.