We have been investigating a novel power generation system based on coal gasification in supercritical water ((Int Commun Heat Mass Trans, 2020, 116, 104706; ASME J Heat Trans, 2021, 143, 024501; Int J Heat Mass Trans, 2022, 194, 123095; ASME J Heat Trans, 2023, 145, 024501). Its advantages over traditional coal-fired systems are zero emission of pollutants and zero extra energy consumption for carbon dioxide separation. Previously, a steam turbine has been used to generate work in this system. However, this method, where the inlet temperature of the steam turbine is ≥ 620°C, is not appropriate for the utilization of the high-grade hydrogen energy generated from the coal gasification process. Therefore, in this work, we investigated the power generation system featuring the combination of coal gasification in supercritical water and gas turbines. The working temperature of the gas turbine matches better the grade of the hydrogen energy, and efficient and cascaded utilization of energy is realized. Referring to the Allam cycle, circulating CO₂ is used to protect the blades of the gas turbine. The addition of CO₂ will not simply sacrifice the efficiency of this system. On the contrary, the net power generation efficiency of this system appears as a peak. Finally, simulations show that the net power generation efficiency can reach 50.9% under 4MPa.