Abstract: Thermochemical reduction of magnesium sulphate with npentane was carried out in an autoclave in the presence of water at high temperature and pressure to simulate the origination of organic sulfur compounds in petroleum from thermochemical sulphate reduction (TSR). The products of 3 phases (gas, oil, and solid) were analyzed by some advanced analytical methods including gas chromatography, microcoulometry, FTIR, and Xray diffraction. The results show that the TSR reaction occurred at 425℃~525℃ with MgO, C, H2S, CO2, and a series of organic sulfur compounds such as mercaptans, sulfoethers, and thiophenes as the main products. The reaction kinetics was studied and the calculated activation energy is 58.0kJ/mol.