Abstract: Effects of methane and carbon dioxide in natural gas on hydrogen production from hydrogen sulfide were investigated by thermodynamic analysis of four H₂S-containing reaction systems. Six main products from the reactions among the three components were taken into consideration. The conversions of the feed and molar fractions of the products in the Gibbs reactor under isotonic and isothermal conditions were calculated by using Aspen Plus simulation software. The effects of the addition and concentration of CH₄ or CO₂ on the conversion of H₂S and the H₂ yield under 0.1 MPa and 400-1 000 ℃ were discussed. The addition of CH₄ or CO₂ could greatly enhance the conversion of H₂S, especially at high temperature and high CH₄ or CO₂ concentration. The addition of CH₄ could also be beneficial for the production of hydrogen while the addition of CO₂ showed the opposite effect. The co-existence of CH₄ and CO₂ in the system could severely inhibit the conversion of H₂S by the overwhelming reforming reaction between CH₄ and CO₂ although the production of hydrogen could be promoted significantly.