The invention discloses an asphalt pavement coating substance and a preparation method thereof, and belongs to the technical field of road construction materials. The technical scheme comprises that the asphalt pavement coating substance is prepared from the following raw materials by weight: 60-80 parts of asphalt, 4-6 parts of an inorganic polymer modifier polyphosphoric acid, 3-9 parts of an acidity regulator, 4-10 parts of an oily viscosity regulator, 2-4 parts of a wear-increasing silicon dioxide aerosol, 2-6 parts of an aqueous viscosity regulator polyethylene glycol, 3-9 parts of a stabilizer, 3-4 parts of an asphalt emulsifier, and 50 parts of water. The invention further specifically discloses the preparation method of the asphalt pavement coating substance. According to the present invention, the asphalt pavement coating substance has advantages of high-temperature performance, low-temperature performance, storage stability, adhesion and wear resistance, especially adhesion and abrasion resistance, and can effectively improve the durability of the asphalt pavement coating.