The invention provides continuous casting protection slag, which contains a calcium-contained compound, a silicon-contained compound and an aluminum-contained compound, wherein the protection slag also contains an addictive; the addictive selects from one or more of compounds which make the melting point and the viscocity in the melting state of the protection slag reduced; the dosage of the addictive makes the melting point of the protection slag reduced to be between 1,160 and 1,260 DEG C, and the viscocity of the protection slag at the temperature of 1,300 DEG C reduced to be between 0.2 and 0.4 Pa.S; and based on oxide, the weight ratio of the calcium-contained compound to the silicon-contained compound of the protection slag is between 0.7 and 1, and the weight ratio of the aluminum-contained compound to the silicon-contained compound is between 0.15 and 0.5. Compared with the prior continuous casting protection slag, the continuous casting protection slag provided by the invention can effectively reduce longitudinal cracks, transverse cracks and subsurface meshy cracks on the surface of casting banks, and the splitting defect rate of steel finished products subjected to casting blank rolling is lower.