A magnesium aluminate bonding agent is characterized in that the magnesium aluminate raw material is formed by the mixture ratio of the following weight percent. The inorganic composition components consist of aluminum sulphate, citric acid, boric acid and magnesia. The product is characterized by carbon free, inorganic combination, no need of high temperature sintering, which can be used after drying at 100 to 200 DEG C, thus greatly reducing the production cost, reducing molten steel pollution and improving the service life. The product can be used in the tank lining, tundish lining, quadrel, air permeable upper quadrel, filling pipe end, drain end, slag dam and steel-tapping hole. The product has the performance of slag adhesion resistance, pretty high high-temperature, medium-temperature and low-temperature strength and has the advantages of reducing molten steel inclusion by more than 90 percent, relieving the labor strength of the workers, shortening masonry labor hour, accelerating the turnover of the molten steel tank for 5-10 times comparing with the existing product. Furthermore, the product has excellent hydration resistance, which can be immersed in the water for 30 days without any change, thus facilitating deposition.