The invention discloses a double-layer tundish covering agent for an ultrathin belt, and relates to the technical field of metallurgy. The upper covering agent and the lower covering agent are hollowgranular products which are subjected to spray granulation. The upper covering agent comprises the following chemical components of, in percentage by weight, 45%-55 wt% of CaO, 18.0-24.0 wt% of SiO2,14.0-18.0 wt% of MgO, less than or equal to 1.9 wt% of Al2O3, 7.5-11.5 wt% of C-solid and the balance inevitable impurities, and the melting point of the upper covering agent is greater than 1450 DEGC. The lower covering agent comprises the following chemical components of, in percentage by weight, 25.0-31.0 wt% of CaO, 27.0-37.0 wt% of SiO2, 13.0-18.0 wt% of MgO, less than or equal to 1.9 wt% ofAl2O3, 13.0-17.0 wt% of (Li2O + Na2O), less than or equal to 0.5 wt% of C-solid and the inevitable balance impurities, and the melting point of the lower covering agent is 1150-1250 DEG C. The product has the advantages that the specific gravity is light, the upper layer is carbon-containing and the lower layer is extremely few in carbon-containing, carbon-increasing is prevented and heat preservation is achieved, the content of Al2O3 in the upper layer and the lower layer is low, the impurities are fully absorbed, the melting point of the upper layer is high, the insulation of the air is isolated, the melting point of the lower layer is low, and rapid melting can be achieved so as to prevent the carbon-containing upper layer from being in contact with the molten steel to increase the carbon.