Isothermal simulation experiments on natural gas-CaSO4-H2O system and natural gas-MgSO4-H2O system were conducted at 450-570 degrees C. Properties of reaction products were analyzed by microcoulometry, gas-chromatography, Fourier transform-infrared spectrometry, and X-ray diffraction methods. Based on the experiments, composition of products, geochemical characteristics, and thermodynamics of natural gas-CaSO4-H2O system were compared with those of natural gas-MgSO4-H2O system. It was found that H2S, CO2, and carbon were the common products of the two thermochemical sulfate reduction systems. In thermochemical sulfate reduction process, CaSO4 was reduced to CaCO3 while MgSO4 was reduced to MgO. At the same reaction temperature, the effect of thermochemical sulfate reduction on natural gas was more intensified in natural gas-MgSO4-H2O system than natural gas-CaSO4-H2O system. With the same temperature and hydrocarbon, MgSO4 more easily participates thermodynamically in the reactions than CaSO4.