The invention belongs to the field of fine chemical engineering, and particularly relates to a method for preparing 2-bromofluorenone by liquid-phase oxidation. The method comprises the following steps: dissolving 2-bromofluorene in N,N-dimethylformamide, adding a catalyst, stirring at 30-40 DEG C under normal pressure, carrying out air oxidation, reacting for 2-4 hours, distilling, filtering, washing with water, and drying to obtain the 2-bromofluorenone. The yield is 96%, and the purity is 99-99.5%. The weight ratio of the 2-bromofluorene to the N,N-dimethylformamide is 1:(3.5-5); and the mole ratio of the 2-bromofluorene to the catalyst is 1:(0.03-0.5). The method has the advantages of mild reaction conditions, lower solvent consumption, high yield, low cost, small environmental pollution, recyclable solvent without further treatment after use and short reaction time, is simple to operate, and is very suitable for large-scale industrial production.