Abstract: High purity MgO precursor was prepared from the brine and industrial ammonia gas (a mix with NH₃:CO₂=5:1).A L16 (45) orthogonal experiment was used to rank the influence of 5 parameters (baume degree, brine and gas ratio, temperature, purification duration and gas adding velocity) on the production. The product was characterized by X-ray diffraction (XRD) and electron microscope (EM). The results suggested that when baume degree was 25. 1, brine and gas ratio was 3:1, temperature was 70℃, purification duration was 1. 5 h, and gas adding velocity was 50 ml/h, the product 4MgCO₃·Mg (OH) ₂·4H₂O was in better condition and was very suitable to prepare high purity Mg O in following step. In addition, the influence of 5 parameters from high to low were brine to gas ratio, baume degree, temperature, gas adding velocity and purification duration.