The invention discloses a method for synthesizing 2-bromo-4-nitroimidazole. According to the method, 4-nitroimidazole (VIII) is taken as a raw material and reacts with a bromide reagent in water under the action of alkali metal bicarbonate, 2,5-dibromo nitroimidazole (XI) is obtained and reacts with an iodo-reagent in an aprotic solvent, and 2-bromo-5-iodo-nitroimidazole (XV) is obtained; 2-bromo-5-iodo-nitroimidazole (XV) further reacts with a phosphorus reduction reagent in an alcohol solvent, and a target product, namely, 2-bromo-4-nitroimidazole (II) is obtained. The method has the main benefits as follows: the overall technology is simple, reaction conditions are mild, the technology is safe, the yield is high, the product quality is high, and industrial production is facilitated.