The invention provides a manufacturing method of magnesium metal. Salt lake bischofite is adopted as the main raw material to manufacture the magnesium metal; a dehydrating agent used in the manufacturing process is thionyl chloride prepared with sulfur as a raw material, the final dehydration process of the salt lake bischofite is achieved through a reaction of a magnesium chloride low-water compound and the thionyl chloride, generation of hydrolysis is avoided effectively, and the high-purity magnesium metal is manufactured through electrolysis. The raw material salt lake bischofite for the magnesium metal and the raw material sulfur for the dehydrating agent are wide in source and low in price, a small amount of chlorine needs to be introduced when a car is driven, and follow-up products serve as intermediate media to participate in circulation so that pollution can be lowered effectively; for example, the relevant sulfur element is converted in the form of different valence states and is finally converted into the thionyl chloride with the wide purpose, the chlorine element is converted into high-purity hydrochloric acid, comprehensive utilization is achieved, and comprehensive economic benefits are high.