High purity magnesium oxide was prepared by using residual brine（main component of magnesium chloride） from Shandong Haihua Group Co.and condensate（rich in ammonium bicarbonate and ammonium carbonate） from calcination unit of sodium carbonate plant as raw materials.The purification and refining process condition of residual brine was determined through experiments：calcium chloride solution was added to residual brine to form calcium sulfate precipitation to remove sulfate from residual brine.When the amount-of-substance ratio of Ca²⁺ to SO₄^2- was controlled to be 0.9~1.0,the sulfate removal effect was better.The purified residual brine and calcined condensate of sodium carbonate were used as raw materials.The reaction was carried out at the reaction temperature of 65 ℃,the stirring speed of 70 r/min and the mass concentration of residual brine magnesium ion of 15 g/L,and then the basic magnesium carbonate was synthesized by pyrolysis and aging.Basic magnesium carbonate was filtered,washed,dried and calcined at 900 ℃ for 2 h to obtain qualified high-purity magnesium oxide.The research results showed that it was feasible to manufacture high purity magnesium oxide from residual brine from Shandong Haihua Group Co.and condensate from calcination unit of sodium carbonate plant.