The invention provides a method for preparing 2, 7-dibromo-4-nitrofluorenone, comprising the followings steps: carrying out oxidation reaction on fluorene to obtain 9-fluorenone; carrying out bromination reaction on the 9-fluorenone to obtain 2, 7-dibromofluorenone; adding the 2, 7-dibromofluorenone and water into a reactor by the weight ratio of 1: 4-6; blending and heating the mixture; when the temperature is 80-90 DEG C, dripping the mixed acid of nitric acid and sulphuric acid rapidly; reacting for 3-5h under reflux, wherein the mol ratio of the 2, 7-dibromofluorenone to nitric acid and sulphuric acid is 1:70-80:60-70; adding water for quenching reaction; filtering; re-crystallizing the obtained solid with tetrahydrofuran and water, and drying the crystal to obtain the 2, 7-dibromo-4-nitrofluorenone. In the bromination and nitrification processes, water is used as solvent. The invention has moderate reaction conditions, simple operation, high total yield (83-88%), low cost, less environmental pollution and easy achievement of industrialization.