The invention relates to a preparation method of 3-(2-bromo propionyl)-spiro[2H-1,3-benzoxazine-2,1'-cyclohexane]-4(3H)-one. The preparation method comprises the following steps of: firstly preparing spiro[2H-1,3-benzoxazine-2,1'-cycloalkane]-4(3H)-one: respectively adding salicylamide, cyclohexanone, a solid acid catalyst and toluene in a reactor, heating and refluxing, stirring and reacting for1-10 hours, cooling to room temperature for precipitating solids, filtering, washing and drying to obtain a solid product; and then preparing 3-(2-bromo propionyl)-spiro[2H-1,3-benzoxazine-2,1'-cyclohexane]-4(3H)-one: respectively adding toluene, a magnetic solid base catalyst and spiro[2H-1,3-benzoxazine-2,1'-cyclohexane]-4(3H)-one in the reactor, dropwise adding halogenated acyl halide, reacting at the reaction temperature of 10-80 DEG C for 1-10 hours, cooling, washing with water, drying, concentrating and crystallizing with isopropyl alcohol to obtain a solid product. Compared with the prior art, the solid acid catalyst and the magnetic solid base catalyst are used in the reaction processes; and the preparation method has the advantages of simple process operation, good technical performance, no environmental pollution and the like.