The invention discloses a high selectivity method for synthesizing moxifloxacin. The method comprises the following steps of: reacting boric anhydride with trifluoro acetic anhydride to obtain a chelant; reacting 1-cyclopropyl-6,7-difluoro-1,4-dihydro-8-methoxy-4-oxo-3-quinolinecarboxylic acid ethyl ester with the chelant, cooling to room temperature, adding ice water, performing suction filtration, and washing a filter cake with water until neutrality to obtain a 1-ethyl-7-chloro-6-fluoro-1,4-dihydro-4-oxoquinoline-3-carboxylic acid methyl ester trifluoroacetic anhydride boronized chelate; and reacting the 1-ethyl-7-chloro-6-fluoro-1,4-dihydro-4-oxoquinoline-3-carboxylic acid methyl ester trifluoroacetic anhydride boronized chelate with (S,S)-2,8-diazabicyclo[4,3,0]nonane to obtain a 1-cyclopropyl-6-fluoro-7-([S,S]-2,8-diazabicyclo[4,3,0]nonane-8-methoxy-4-oxo-1,4-dihydro-3-quinolinecarboxylic acid ethyl ester trifluoroacetic anhydride boronized chelate, recycling a solvent under reduced pressure, adding alkali, refluxing, discoloring, filtering, freezing, performing suction filtration, and drying a filter cake. The method is simple, mild in conditions, and high in selectivity, avoids difficultly separated impurities, is high in reaction yield and product purity, and is suitable for industrial production.