The invention relates to high-sodium low-fluorine covering slag, which is prepared from raw materials of wollastonite, limestone, quartz sand, fluorite, bauxite, manganese carbonate, magnesia, hydrous borax, industrial soda, lithium carbonate, and carbonaceous materials, and the chemical components of the covering slag meets the following weight percentage: more than 30 and less than 34 percent of CaO, more than 30 and less than 38 percent of SiO2, more than 12 and less than 25 percent of Na2O, less than 4 percent of MgO, less than 8 percent of MnO, less than 4 percent of B2O3, less than 1.5 percent of Li2O, less than 4 percent of Al2O3, less than 2 percent of F, more than 4 percent and less than 10 percent of C, and the balance being impurities. In the covering slag, the ratio of sigma CaO to the SiO2 is controlled to between 0.8 and 1.15 to ensure that the fused mass of the covering slag does not separate out crystals at high temperature and liquid slag in a slag film can lubricate a casting blank. Aiming at that the content of fluorine has adverse influence on environment and equipment, the invention adopts high-sodium low-fluorine continuous casting covering slag which not only can meet the requirement of coordinated control of heat transfer and lubrification of a continuous casting covering slag for crack sensitive steel to cast casting blank with good surface quality, but also can reduce the fluorine content in air and secondary cooling water, thus the air pollution is reduced and the corrosion of fluorine-contained water to equipment is reduced.