A potential energy-based power generation system comprises a first reservoir disposed on an upper part of a building and configured to reserve water, a second reservoir located underground of the building and configured to reserve the water, a small hydro power generation unit including a small hydro power generation turbine to generate the power, a fuel cell power generation unit disposed at one side of the first reservoir and configured to generate the power using the hydrogen gas, an electrolysis device disposed in the second reservoir and configured to perform electrolysis for decomposition of the water into the oxygen and hydrogen gas by using the external power or the power generated by the small hydro power generation unit.