Addressing the issue of high energy consumption in electrically-driven working fluid pumps within conventional organic Rankine cycle (ORC) power generation systems, this study proposes a novel ORC system incorporating an alternating pressure type thermal-gravitational pumping module. Through analysis of the effects of heat source temperature, cold source temperature, and pumping module parameters on system performance, it is found that increasing the heat source temperature elevates the net output power and the vapor consumption ratio of the module. Conversely, raising the cold source temperature reduces net output power and system efficiency while exhibiting negligible impact on the vapor consumption ratio. Furthermore, the vapor consumption ratio of the module can be reduced by expanding the supply volume range, or increasing the initial volume ratio within a fixed supply volume range, thus improving overall system performance. By comparing performance with the conventional ORC system, the optimal operating conditions for the novel system are identified. This research provides a theoretical basis and reference for the design and optimization of power generation systems driven by low-grade thermal energy.