The invention relates to a method for synthesizing moxifloxacin hydrochloride. The method is characterized in that: moxifloxacin hydrochloride is precipitated from solution according to solubility difference of the moxifloxacin hydrochloride in sodium chloride solution with different concentrations so as to fulfill the aim of separation. The method particularly comprises the following steps of: adding sodium chloride into moxifloxacin hydrochloride-containing aqueous solution; stirring to crystallize; filtering; drying; recrystallizing with water; filtering; and drying to obtain the moxifloxacin hydrochloride. The method is simple and convenient in operation; the product has high purity; a single impurity is less than 0.1 percent; the total impurities are less than 0.2 percent; and the method is suitable for industrialized production.