Abstract: A thermodynamic model for gas-solid reduction reactions of iron oxides was established based on the minimized Gibbs free energy principle. On the basis of the model calculation results, the equilibrium diagram for the gas-solid reduction reactions of iron oxides was graphed; the equilibrium results are in good agreement with the reported experimental data. Comparison with the data from common metallurgical books and thermodynamic databases indicates big differences in thermodynamic data from different references. Thermodynamic equilibrium was investigated for the stepwise reduction sequence of iron oxides. The thermodynamic equilibrium was calculated for iron oxide reduction using CO-H₂ mixtures as a reducing agent. According to the calculation results, the formula for the gas utilization ratio η_总 in the equilibrium state was deduced, and the three-dimensional equilibrium diagram of iron oxide reduction using CO-H₂ mixtures was graphed. As compared with the reported experimental data indicates the correctness of calculation results.