Abstract:with carbide slag and magnesium chloride as raw materials, mixture of calcium hydroxide and magnesium hydroxide was obtained by chemical synthesis method. The mixture was calcined at low temperature to prepare calcined dolomite for magnesium preparation by Silicothermic Method under vacuum condition with addition of ferrosilicon and fluorite. The results show that this technical route is feasible, with yield of magnesium almost equal to Pidgeon Process. The optimum conditions include Ca/Mg molar ratio of calcined product of 0.85, calcinations temperature of 850 ℃, and time of 1.0 h.