A geothermal energy storage/converting system utilizes hot water and pressure, such as steam, generated by the geothermal heat/ground water to store energy and/or generate electricity. The system utilizes a motion of a piston, driven by steam generated by geothermal heat, to control movement of an amount of water, which is used to store the energy by compressing gas as energy storage. When electricity is needed, the compressed gas provides a force to push the stored water to drive a hydrogenerator to generate electricity. In a geothermal energy converting embodiment, system utilizes a motion of a piston, driven by steam generated by geothermal heat, to control movement of an amount of water to drive a hydrogenerator to generate electricity.