The invention relates to a roofing polyurethane modified asphalt waterproof paint and a preparation method thereof. The paint is prepared from a polyurethane prepolymer, 90# petroleum asphalt, modified nano calcium carbonate, vinyl trichloro silane, a tackifier, n-butyl acetate, citric acid, dibutyltin dilaurate, polyoxyethylene polyoxypropylene ether, fumed silica and a heat insulation material.The preparation method includes: using the polyurethane prepolymer and modified nano calcium carbonate to modify 90# petroleum asphalt; then adding vinyl trichloro silane, citric acid and n-butyl acetate, and stirring the substances evenly; then adding fumed silica, the tackifier, dibutyltin dilaurate and the heat insulation material, and stirring the substances evenly; then adding polyoxyethylenepolyoxypropylene ether and performing further stirring till no powder flotation; subjecting all the materials to shearing again on a high speed shearing machine until the 90# petroleum asphalt and the other materials are evenly dispersed, thus obtaining the product. The product has the advantages of good weather resistance, good heat insulation effect and good dispersibility.