In order to improve the extraction rate of Magnesium Oxide and reduce the energy consumption of products. To improve the quality of products and increase the variety of products, the double subtraction carbonization process mainly changed the carbonization conditions and reduced the production process with high energy consumption. The purified lime emulsion was carbonized under specific conditions, and the 80 - 90% MgO was dissolved and the supersaturated solution of magnesium carbonate containing 20~30 grams / liter of MgO was formed. Under the special conditions, the basic magnesium carbonate solution was obtained at 20~30 degree by rapid pressure filtration under certain conditions. This basic magnesium carbonate filter cake contains only 50 - 60% moisture. The light Magnesium Oxide products were calcined.