The invention relates to a synthesis method of 2,4,6-tris(2,4-dihydroxyphenyl)-1,3,5-triazine, belonging to the technical field of fine chemical synthesis. The synthesis method comprises the following steps: heating an acidic ionic liquid which is used as a solvent and catalyst and resorcin and cyanuric chloride which are used as raw materials to 10-150 DEG C while stirring, reacting for 1-15 hours, carrying out post treatment, evaporating to remove the solvent while depressurizing, and refining. By adopting the above technology and using the acidic ionic liquid as the solvent and catalyst to prepare the product through a one-pot method, the method has the advantages of convenient operation process, mild reaction conditions and convenient post treatment; for the product, the yield is as high as 90% or above, the purity is high, the HPLC (High Performance Liquid Chromatography) is greater than or equal to 99.5%, and the melting point is higher than 300 DEG C; and the recovered acidic ionic liquid can be repeatedly used. Thus, the synthesis method causes less three wastes and reduces the environment pollution, thereby being an economical, practical and environment-friendly technology.