The article focuses on the development of a thermodynamic model for hydrogen production from rice straw through supercritical water gasification (SCWG) technology. SCWG is a process with the potential to efficiently and cleanly convert biomass, such as rice straw, into hydrogen gas. The model was designed to predict the outcomes and boundaries of the gasification process utilizing the Gibbs free energy minimization principle. It analyzed the equilibrium distribution of gasification products under various operating conditions like temperatures ranging from 400 to 1200 °C, pressures between 20 to 50 MPa, and rice straw concentrations of 5 to 40 wt%. Notably, the study pointed out that due to the unique characteristics of supercritical water, coke formation might be avoided under certain thermodynamic constraints. The results indicated that optimizing the process parameters, such as higher temperatures, lower pressures, and increased biomass concentrations, could enhance hydrogen production. For instance, the highest hydrogen yield of 47.17 mol/kg was achieved at 650 °C, 25 MPa pressure, and a 5 wt% rice straw concentration. Additionally, the research highlighted the importance of an absorptive process in the SCWG of rice straw to produce high-calorific value hydrogen. It was also noted that the addition of small amounts of oxygen (ER < 0.2) could sustain the energy self-sufficiency of the SCWG process. Overall, the study provides valuable insights for guiding experimental activities related to rice straw SCWG. By offering a detailed thermodynamic model and emphasizing the significance of process parameters, the research contributes to advancing the efficient production of hydrogen from biomass sources like rice straw.