A preparation method of the Toltrazuril is provided. The Toltrazuril is the 1-[3-methyl-4-(4- Trifluoromethylthiobenzoxy) benzyl]-3-methyl-1, 3, 5, -triazine-2, 4, 6(1H, 3H, 5H)-trione. The methyl sulfide chloro compounds, fluoro-compounds, amides, phenol, methyl nitrate chlorobenzene, benzene aether, ammonia benzene aether, isonitrile acid ester and methyl urea from the reactions of 4-nitrochlorobenzene, sulfur, sodium sulfide and dimethyl sulfate. The detailed preparation is that reaction 1: the methanol of 410g and 4-nitrochlorobenzene of 158g are mixed and heated until soluble and are added with sulfur, sodium sulfide and methanol mixed liquor by drops, and kept for 2h under temperature of 60 DEG C. to 65DEG C.; reduce the temperature, add water of 880g and add dimethyl sulfate of 192g; during the period, the pH value of the sodium hydroxide is adjusted over 9, and the methyl sulfide of 153.6 is gained by filtering after reaction with yield of 91.1 per cent.