Abstract: To study the chemical mechanisms of the formation of high H2S concentrations in natural gas, thermal simulation experiments on the reaction between natural gas and solid calcium sulfate were carried out in an autoclave under high temperature and high pressure. Properties of the reaction products were analyzed by gaschromatogram, microcoulometry, Fourier transforminfrared spectrum and X-ray diffraction methods. Thermodynamic characteristics of thermochemical sulfate reduction (TSR) and the reaction kinetics were investigated. It was found that natural gas could react with solid calcium sulfate under high temperatures, and that hydrogen sulfide, carbon dioxide, calcium carbonate, water and carbon are the main products. TSR of natural gas with solid calcium sulfate is thermodynamically possible and high temperature is favorable to the reaction. The reaction with longchain hydrocarbons can take place more easily than shortchain ones. According to the reaction model, the activation energy of the reaction is 96.824kJ/mol.