The invention relates to a method for producing 9-fluorenone, comprising the following steps of: (1) feeding industrial fluorine as a raw material and methylbenzene as a solvent into a reaction kettle according to the weight ratio of 1:(6-8) with quaternary ammonium salt as a catalyst; heating the mixture to 40-80DEG C; adding the catalyst after the raw material is completely dissolved at the addition of 5-20 percent of industrial fluorine; introducing the air according to 2-3m<3>/h of each kilo of industrial fluorine and reacting under the condition of 40-80DEG C for 2-5h; (2) after the reaction is ended, pouring a reactant into a distillation kettle for distillation at normal temperature, recovering the solvent and obtaining an industrial fluorine crude product from the bottom of the kettle; and (3) recrystallizing the crude product with the solvent to obtain fluorenone with the content of 99 percent. The method has the advantages of simple process flow, fewer reactants and low cost, is easy to control and can be widely used for producing the fluorenone; and the finished products prepared by the method have favorable quality.