The invention relates to a synthesis method of 2,4,6-trimethyl-m-phenylenediamine. The method is characterized by comprising the steps of: (1) dropwise adding mixed acid into mesitylene for nitration and generation of 2,4,6-trimethyl-m-dinitrobenzene; after the reaction, standing for layering; neutralizing and washing an obtained organic layer to obtain 2,4,6-trimethyl-m-dinitrobenzene; (2) adding the 2,4,6-trimethyl-m-dinitrobenzene the obtained the step (1) to an autoclave, then adding a catalyst and a solvent, replacing the air in the autoclave with nitrogen gas, introducing hydrogen gas and conducting hydrogenation reduction to form 2,4,6-trimethyl-m-phenylenediamine, wherein the hydrogenation temperature is 50-120 DEG C, and the catalyst is a nickel catalyst; discharging hydrogen after the hydrogenation reduction, discharging the materials, removing methanol, cooling, crystallizing, and filtering to obtain the 2,4,6-trimethyl-m-phenylenediamine. The method has the advantages of short synthetic route, high product purity, high yield, few reaction steps, and long usage period of a hydrogenation reduction catalyst.