The invention discloses a gravity generator, comprising a generator and a storage battery and further comprising a reversed buoyancy piston device and a cylinder body, the buoyancy piston device is placed in the cylinder body; an inner wall of the cylinder body is provided with four upper limiting power supply joints and four lower limiting power supply joints, an outlet is arranged below the cylinder body, a pressure storage tank is arranged at the outside of the cylinder body and is connected with the generator and the outlet via pipelines respectively, the pipeline by which the pressure storage tank is connected with the outlet is provided with a one-way valve; the buoyancy piston device is communicated with the generator via a return conduit. Such a gravity generator does not consume the mineral reserves on the earth, is not limited by time and weather, is free from the exhaust of waste gas and the pollution to environment, and can ceaselessly implement the power generation.