The invention relates to a coating material used for heat treatment technology before rolling a billet of spring steel. The coating materials is directly sprayed onto the billet at the temperature below 500 DEG C and has good blocking property, a dense microcrystal glass layer is formed on the surface of the billet at a high temperature section, mutual diffusion of carbon and nitrogen can be effectively blocked; meanwhile, ingredients in the coating can obviously reduce high temperature activity of carbon atoms in steel, improve decarburization sensibility of the steel and effectively alleviate high temperature decarburization problem of the spring steel, and the dense microcrystal glass layer can naturally strip off in a subsequent cooling process. The coating can effectively prevent decarburization problem of the spring steel in a heat treatment process at the temperature of 950-1150 DEG C, self-stripping capability is high, the coating is safe and convenient to use, heating is not influenced, cost is low, and no pollution is produced.