In this paper, thermal sulfate reduction was conducted in autoclave under certain temperature and pressure conditions. Gaseous products were analyzed using gas chromatography and microcoulometry. Total sulfate of the liquid products was analyzed by microcoulometry. Solid products were analyzed by FT-IR and X-ray diffraction and the reaction kinetics was investigated. The activation energy of the system of Tuha crude oil and magnesium sulfate was 53.26 kJ/mol, while activation energy of Shengli crude oil and magnesium sulfate was 57.91 kJ/mol. It showed that content of LSC in the crude oil effected on the extent of reaction. The higher content of LSC, the stronger activity of TSR. In addition, the LSC has certain effect on the initial temperature of the TSR. LSC leaded to form reactive intermediates sulfate ester in the process of TSR. Sulfate esters were relatively unstable and would be expected to oxidize the hydrocarbon.