The invention discloses a hydraulic device, especially a device for developing and using potential energy of fresh water which has wide adaptability and can save and increase energy. The device is characterized in that a water getting device is connected to an overground total pool through a turbid water pipe, the upper part of the overground total pool is provided with a main communicating pipe,the other end of the main communicating pipe is connected with a first overground reservoir, the first reservoir is connected with a second overground reservoir through an upper communicating pipe and a lower communicating pipe, the second reservoir is connected with two to eight clear water pipes, the clear water pipes are connected with at least two safe pools, each safe pool is connected with at least two user reservoirs through pipelines, and the safe pools can be provided with power generating equipment for generating electricity. Compared with the prior art, The device of the invention can prevent fresh water in rivers from flowing into the sea, effectively use the water, and save energy, has good economic benefit, and can be connected to power generation device for generating powerand generating electricity energy.