Abstract: A subterranean geothermal power generation system is disclosed herein, comprising a closed cavity, a temperature differential mechanical power generation device, an electric power generation device and a heat conduction module. The mechanical power generation device with a heat source end and a cold source end and the electric power generation device are integrated into the cavity. The heat source end is exposed from the cavity for contacting with a heat source in the well; the cold source end and the electric power generation device are located in the cavity. A heat conduction fluid is filled into the cavity, the heat conduction module extends from the cavity to the outside of the well. Accordingly, a temperature difference between the cold source end and the heat source end is created to enable the mechanical power generation device to mechanically drive the electric power generation device to generate electricity.