Preparation method of casting coating

The invention discloses a preparation method of a casting coating. The preparation method of the casting coating relates to the technical field of casting. The casting coating is prepared from the following raw materials in parts by weight: 50 to 60 parts of zircon powder, 20 to 25 parts of forsterite powder, 8 to 12 parts of bauxite, 6 to 10 parts of activated bentonite, 0.8 to 1.2 parts of calcium lignosulphonate, 2 to 3 parts of silica sol, 0.1 to 0.2 part of sodium sulfate, and 2 to 3 parts of white emulsion. The preparation method comprises the following concrete steps of A, weighing the raw materials; B, putting the zircon powder, the forsterite powder and the bauxite into a mixing and grinding machine, and mixing and grinding to obtain a mixed base material; C, adding the activated bentonite, the calcium lignosulphonate, the silica sol, the sodium sulfate and the white emulsion into the mixed base material, and adding water for mixing and grinding; and D, pouring the material obtained through the step