A hydraulic power generating system is disclosed. The hydraulic power generating system includes a looped rail, a plurality of pulleys moving along the looped rail, a plurality of water receiving plates, each being installed to each of the pulleys, side plates which are hingedly coupled to left and right side portions of each of the water receiving plates by hinge shafts, and spread adjusting devices which make the side plates spread against a direction of water flow. Accordingly, since the spread direction of the side plates hingedly coupled to both side portions of the water receiving plate can be changed forward and backward according to the direction of water flow so as to receive a larger amount of water, efficiency in generating power using water energy increases.