The invention discloses high-viscosity continuous casting protective slag for solving slag inclusion on the surface of low-carbon steel. The protective slag comprises the following raw materials by weight percent: 0%-7% of glass powder, 50%-70% of premelting material, 5.5%-8.5% of fluorite, 4%-8% of dietary alkali, 3% of N330 carbon black, 3.5% of graphite, 0%-3% of R agent, 0.5-2% of lithium carbonate, 2%-5% of manganese carbonate, 2%-5% of magnesite, 3%-7% of bauxite, 1%-3% of cryolite, 1%-3% of adhesive, and 0.3%-1% of water-reducing agent. By utilizing the high-viscosity continuous casting protective slag, mainly on the basis of CaO and SiO2, a certain amount of fluxing agents such as the lithium carbonate, the fluorite, the dietary alkali and the like and a certain amount of carbon materials such as carbon black and graphite are externally added, thus the viscosity is improved and the surface tension is increased; and under the same technique condition, slag inclusion on the surface of a steel billet can be effectively prevented.