Abstract: The operation characteristics of the hydrogen oxidation reactor in the novel combined hydrogen production and power generation system based on coal gasification in supercritical water were preliminarily investigated. A plug flow reactor model was established using Aspen Plus to simulate the hydrogen oxidation reactor for the novel supercritical water/carbon dioxide hybrid working fluid, and the effects of reaction temperature and components flow rates on hydrogen oxidation were studied. It is shown that the primary chemical reactions in the reactor are the oxidation of hydrogen, methane and carbon monoxide, and that methane oxidation takes place easier than hydrogen oxidation under oxygen-deficient condition. Based on the simulation results, the improvement measures were proposed to solve the problems of the residual hydrogen at the exit of the reactor and temperature nonuniform in the reactor, providing a reference for improving the hydrogen utilization efficiency as well as the safety of turbine with the hybrid working fluid.