Abstract: Thermodynamic equilibrium analysis was performed on methane autothermal reforming to generate hydrogen by using the minimization of Gibbs free energy. Effects of operation parameters such as molar ratios of steam to methane (W/M), air to methane (A/M) and adiabatic temperature on the reforming process were studied. Results showed that the optimal W/M is around 2.5~3.5 and molar oxygen to methane between 0.4 and 0.7. Thus the reforming temperature lays between 700℃ and 850℃ and H2 generating per mole methane is around 2.17mol～2.23mol. Taking example for the 1.5 of W/M, possible formation or conversion mechanisms were deduced for different constitutes under different A/W through the simulating calculations. The thermodynamic equilibrium calculations provide optimal operation parameters for methane autothermal reforming to generate hydrogen.