The invention relates to a 1,3,5-tri-mercapto methyl benzene compound and a preparing method thereof. The preparing method comprises the steps that 1,3,5-tribromomethyl phenyl reacts with thiourea, ethanol-n-butylacetate serves as a solvent to prepare isothiourea salt, and then sodium hydroxide is added for hydrolysis; trichloromethane is used for extraction, attapulgite is used for adsorbing impurities, and high-purity colorless 1,3,5-tri-mercapto methyl benzene is obtained. The 1,3,5-tri-mercapto methyl benzene compound prepared with the method is high in purity and refractive index and also has the advantages of being high in transmittance and the like, wherein the light transmittance of obtained 1,3,5-tri-mercapto methyl benzene is higher than or equal to 89%, the refractive index is higher than or equal to 1.65, and the yellow index is smaller than or equal to 1.