The invention provides a magnesite dolomite brick used in the fields of steel plant, non-ferrous smelting industry and building material industry. The magnesium dolomite brick contains the following chemical components in weight percentages: more than or equal to 48% of Mg, 33% of CaO, less than or equal to 2.9% of Al2O3, more than or equal to 12% of SiO2, and less than or equal to2.5 % of Fe2O3. The final product (natural dolomite) is obtained by crushing, sieving, mixing, stirring, adding binders, homogenizing, drying and sintering at a temperature more than or equal to 1700 DEG C. The product is inactive to hydration and is stable for storage without oil immersion or wax immersion treatment or sealed package, and is a new product developed from local dolomite resource. The product has the advantages of high CaO content, inactivity to hydration, high melting point, high refractoriness under load, good fire resistance, less plastic deformation at high temperature, good stability to heat and shock, large crystallization strength, good resistance to shear stress, slag corrosion and erosion, and strong chemical stability to alkaline steel slag and iron-containing furnace slag. The magnesium dolomite brick is used as substitute for magnesia-chromite brick and magnesia carbon brick.