The invention belongs to the field of chemical synthesis and especially relates to a preparation method for benzene dimethylene diisocyanate. The method comprises the following steps: a) performing acylating chlorination reaction on triphosgene and m-xylylenediamine in a solvent under the existence of catalyst and acid-binding agent, thereby acquiring reaction liquid, wherein the catalyst contain trimethylchlorosilane and/or hexamethyl-disilazane and the acid-binding agent contains one or more of triethylamine, pyridine and dimethyl formamide; b) heating the reaction liquid and reacting, thereby acquiring benzene dimethylene diisocyanate. According to the invention, triphosgene and m-xylylenediamine are used as initial raw materials, the benzene dimethylene diisocyanate is prepared in two steps under the existence of catalyst and acid-binding agent and the technology is simple. According to the method provided by the invention, the benzene dimethylene diisocyanate can be prepared under normal pressure, the reaction condition is easily controlled and the safety factor is high. Besides, the preparation method provided by the invention is higher in product yield.