The invention discloses a method for synthesizing 2,5-dibromo phenylacetic acid. The method comprises the following step: by taking isatin as a raw material, carrying out carbonyl reduction, 5-site bromo reactions and diazotization hydrolysis reactions, thereby obtaining 2,5-dibromo phenylacetic acid, wherein the step of carbonyl reduction is carried out through catalytic hydrogenation reduction;the step of 5-site bromo reactions is carried out with NBS (Bromo-Succinimide) as a bromo agent; and the step of diazotization is carried out with a sodium nitrite/hydrobromic acid system. HBr/cuprousbromide is adopted as a hydrolysis bromo agent. The method has the advantages of being wide in raw material source, mild in reaction condition, high in yield, excellent in quality, low in finished product cost, and the like.