Abstract: Magnesium sulfate heptahydrate was made from salt lake magnesium chloride and sulfuric acid, then anhydrous magnesium sulfate was obtained from magnesium sulfate heptahydrate by dehydration, and finally high-purity magnesia was prepared from anhydrous magnesium sulfate by natural gas reduction pyrolysis. The effects of pyrolysis temperature, pyrolysis time, particle size, and gas flow rate on the conversion rate of magnesium sulfate were investigated by single factor experiment. These experimental parameters were optimized by orthogonal experiment. The reduction pyrolysis product was analyzed and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The optimal experimental parameters are as follows:the pyrolysis temperature is 1000℃, the pyrolysis time is 30 min, the particle size of anhydrous magnesium sulfate is 75 μm, and the flow rate of natural gas is 25 mL·min^-1. The pyrolysis temperature is the main factor which influences the conversion rate. Under the optimal condition, the conversion rate of magnesium sulfate reaches 99.27%, and the purity of magnesia is 99.5%. The unimolecular MgO features well-distributed particle size, porous and fluffy surfaces, and high specific surface area.