Abstract: The temperature of newly discharged reduced magnesium slag can reach 1200℃, and the rest heat has high reuse value. Simulation of waste heat of magnesium slag preheating crude magnesium was performed using finite element software. The heat distribution and heat transfer law of crude magnesium under different crucible positions were studied from the aspects of heating mode and heating time. The mobile crucible was optimized into an S-shaped heating tube to improve the heating efficiency. By optimizing the design, the crude magnesium is changed into 850℃ liquid, which effectively improves the waste heat utilization efficiency of the magnesium slag.