The invention belongs to the field of organic chemical synthesis and in particular relates to a preparation method of terephthaloyl chloride. The preparation method comprises the following steps: under irradiation of an LED (light-emitting diode) light source, introducing excessive chlorine to p-xylene to react to obtain a 1,4-bis(trichloromethyl)benzene crude product; enabling the 1,4-bis(trichloromethyl)benzene crude product to react with p-phthalic acid in the presence of a catalyst until no hydrogen chloride is released and carrying out vacuum distillation on an obtained reaction liquid to obtain terephthaloyl chloride. The preparation method has the beneficial effects that the preparation method has the advantages of easily obtained raw materials, low cost, easiness in tail gas treatment, and the like and is suitable for industrial production; the melting point, purity and yield of prepared terephthaloyl chloride are respectively 82-83 DEG C, more than 99.9% and more than 95%; any solvent is not needed to be mixed, the catalyst is recycled, and the high purity of the product is kept.