The invention belongs to the field of polymer materials, relating to a method for synthesizing acetoacetate ester modified polymer. The method comprises the following steps: taking polymer containing hydroxyl and micromolecule acetoacetate ester as raw materials, and performing reaction under the condition of microwave irradiation; and the equation is shown in the specification, wherein R2(OH)n is polymer containing multi-hydroxy. The invention synthesizes the polymer of which side chains or chain ends have a plurality of acetoacetate ester groups by the process of catalytic ester exchange. The synthetic method has the advantages of high efficiency, mild synthetic method and high safety. In addition, in the method, the catalyst can be added, thereby improving synthetic efficiency; the synthetic rate of the method is greatly improved compared with the prior art; and the reaction time is shortened to 2-30min.