Gasification of biomass in supercritical water is a successful technology for hydrogen production especially by using wet biomass. The whole process, from feeding to purification of hydrogen, consists of a lot of equipment, such as pumps, heat exchangers, heaters, reactors, etc. Because the main reactions take place in the gasification reactor; the gasifier is the most important equipment of the process. hi this article, a thermodynamic model, including chemical equilibrium in, the reactor that is based on Gibbs free energy minimization, is developed to estimate equilibrium composition for gasification of biomass in supercritical water for hydrogen production. For this analysis, we use three types of equations of state, including Peng-Robinson, statistical associating fluid theory equation of state, and a new equation of state. We consider glucose as a model of real biomass. The results of each equation of state are compared with the experimental data. The predicted results show good agreement with the experimental data and it shows that the product gases consist of hydrogen and carbon dioxide more often and methane and carbon monoxide less often. Finally, effects of temperature, pressure, and feedstock concentration are investigated on amount of hydrogen production.