The invention relates to a preparation method of a high-chromium brick coating, belonging to the technical field of high-chromium bricks. The high-chromium brick comprises a high-chromium brick body and a high-chromium brick coating. The method comprises the following steps: adding an adhesive into medium-grain-size zirconium oxide, medium-grain-size chrome oxide green and medium-grain-size active aluminum oxide micropowder in the high-chromium brick coating, uniformly mixing, and uniformly spraying the high-chromium brick coating mixture on at least one surface of a high-chromium brick, wherein the spraying surface is a counter fire surface; and baking and drying the sprayed high-chromium brick, and firing at high temperature to obtain the coated high-chromium brick. The protective coating can effectively lower the apparent porosity of the high-chromium brick, enhance the surface density of the high-chromium brick, obviously improve the scouring permeability of the high-chromium brick and prolong the service life of the high-chromium brick.