The invention discloses a method for synthetizing 7-fluorine-6-amido-2H-1,4-benzoxazine-3(4H)-ketone. According to the method, 2,4-difluroaniline is used as raw materials; the 7-fluorine-6-amido-2H-1,4-benzoxazine-3(4H)-ketone (a flumioxazin intermediate) is prepared through hydroxy substitution, etherification, nitration and hydrogenation reduction reaction. The synthesis method provided by the invention has the advantages that the 2,4-difluroaniline is used as the raw materials; the price is low; the obtaining is easy, so that the production cost is reduced to a certain degree; the intermediate I can react with methyl chloroacetate to form rings without high-pressure hydrogenation reaction, so that the reaction risk is reduced; the nitratlon reaction is easy to control; side reaction is reduced; the impurities are few; the yield is improved; a hydrogenation reaction catalyst can be recovered; the cyclic use is realized; the cost is reduced; in addition, the raw materials are cheap and can be easily obtained; the reaction is mild; the operation is simple and convenient; the scale production is favorably realized.