NOVELTY - Synthesis of toltrazuril, involves: (a) putting trifluoromethylthiophenol, potassium carbonate and dimethyl sulfoxide into a reactor; (b) adding substance 3 obtained in (a), the catalyst and the reaction solvent; (c) mixing bi-trichloro methyl carbonate and solvent, and adding substance 4 obtained in (b); and (d) placing methylurea and diethyl carbonate into reactor to mix.    USE - The method is useful for synthesizing toltrazuril (claimed).    ADVANTAGE - The new technique for synthesizing toltrazuril in the invention is simple to operate, simple in needed device, less in pollution, easy to obtain material, low in cost, high in yield; its total yield of product is about 50%.    DETAILED DESCRIPTION - Synthesis of toltrazuril, involves: (a) putting trifluoromethylthiophenol, potassium carbonate and dimethyl sulfoxide into a reactor, adding 2-chlorine-5-nitrotoluene solvent solution under 70-100 degrees C in 0.5-2 hours, where the mol ratio of the trifluoromethylthiophenol, potassium carbonate and dimethyl sulfoxide is 1:1-1.4:2-10:0.8-1.2, the mol ratio of the 2-chlorine-5-nitrotoluene and the solvent is 1:1.5-5, after adding, reacting for 2-6 hours at 90-180 degrees C, then, reducing pressure to evaporate out solvent, adding icy water after finishing evaporating, filtering, using petroleum ether to re-crystallize after drying filter cake, obtaining substance 3, represented by Formula 3; (b) adding the substance 3 obtained in (a), the catalyst and the reaction solvent according to mol ratio of 1:0.05-0.5:20-100 into reactor, reaction solvent is C1-C4 low degree fatty alcohol, aerating hydrogen under 50-100 degrees C until finishing thin layer chromatography (TLC) detection reaction, cooling, reducing temperature to indoor temperature, filtering out the catalyst, reducing pressure for filtrate to evaporate out the reaction solvent, collecting 160-166 degrees C/2 mmHg distillate from residuum, solidifying after cooling, obtaining substance 4, represented by Formula 4; (c) mixing bi-trichloro methyl carbonate and solvent according to mol ratio of 1:10-30 to obtain mixing liquid, dropping the substance 4 obtained in (b) into the mixing liquid under the temperature of - 10 to - 5 degrees C, where the mol ratio of the substance 4 compared with the bi-trichloro methyl carbonate is 1:0.5-1.5, after finishing dropping, keeping temperature under - 5 to 0 degrees C for 1 hour, then, lifting temperature and reflowing for 4-8 hours, evaporating out the solvent, collecting 142-150 degrees C/40 Pa distillate from residuum, solidifying after cooling, obtaining substance 5, represented by Formula 5; and (d) placing methylurea and diethyl carbonate into reactor to mix, keeping temperature for 2 hours under 85-90 degrees C, reducing temperature to 70 degrees C, adding the substance 5 obtained in (c), reacting for 2-6 hours under 70-110 degrees C, reducing temperature to indoor temperature, adding proton alkali solution into the reactor, where the mol ratio of the substance 5, the methylurea, the proton alkali and the diethyl carbonate is 1:1-1.2:2-4:3-15, reacting for 2-6 hours under normal temperature, raising temperature to 80-120 degrees C, reflowing reacting for 8-16 hours, reducing pressure to evaporate out solvent, after cooling residue, adding the residue into water whose volume is 4-10 times of that of the residue, using 20% of dilute sulfuric acid to adjust pH value to 7, separating out white solid, filtering, drying, using alcohol solvent to re-crystallize, obtaining toltrazuril. Structures 3-5,