Abstract: High pressure water can be used to separate CO₂ from H₂ after the process of hydrogen production by biomass gasification in supercritical water.Based on the modified UNIFAC, SRK equation of state and the MHV2 mixing rule, a gas-liquid equilibrium model of high pressure water absorption of biomass gasification product gas was proposed.The influence of the main parameters, such as temperature and pressure, on the separation process was investigated.The predicted results showed that with increasing pressure the molar fraction of H₂ increased but H₂ yield decreased in the gas phase.The molar fraction of CO₂ decreased sharply with increasing pressure.With increasing temperature, the molar fraction of H₂ in gas phase decreased and the molar fraction of CO₂ increased.H₂ yield in the gas phase increased with the increasing temperature.But CO,CH₄,C₂H₄ and C₂H₆ could not be separated from H₂ from gas phase products by high pressure water absorption.