Abstract: High-purity magnesium oxide was prepared by calcining magnesite which mixed with anhydrous magnesium chlo- ride at a lower calcination temperature.The thermal decomposition of mixed powders was analyzed by thermogravimetric anal- ysis and dynamic thermogravimetric analysis（TG-DTA）.The prepared product was also characterized by X-ray diffraction （XRD），scanning electronic microscope（SEM），and purity analysis.Compared with the traditional method，the results showed that adding magnesium chloride can effectively remove calcium.Through mechanism discussion，because of chloride ion′s penetration，magnesium chloride played a role of partition to magnesite，it made magnesite′s specific surface area increase and calcination temperature decrease，which got the effect of energy-saving and cost-reducing.The product′s purity could reach 99.3% and calcium impurity mass fraction reduced to 0.07%，when calcination temperature was 650 ℃ and calcination time was 1 h.

Key words: magnesium chloride, energy-saving and cost-reducing, high-purity magnesium oxide, magnesite