NOVELTY - Improving the chemical purity of moxifloxacin industrial side chains involves: (1) purification of crude moxifloxacin side chain before synthesis; (2) obtaining a white crystalline side chain double moxifloxacin hydrochloride; and (3) obtaining the moxifloxacin side chain purification products with chemical purity by GC analysis of 99%.    USE - The method is useful for improving the chemical purity of moxifloxacin industrial side chains (claimed).    ADVANTAGE - The method efficiently improves the chemical purity of the moxifloxacin product.    DETAILED DESCRIPTION - Improving the chemical purity of moxifloxacin industrial side chains involves: (1) purification of crude moxifloxacin side chain before synthesis: taking moxifloxacin benzyl side chains, adding methanol, 5% palladium (Pd)-carbon (C) is added to the autoclave, heating to 90 degrees CC, hydrogen pressure of 90 kg, maintaining for 16 hours, after completion of the reaction, removing by filtering Pd-C, the filtrate is evaporated to dryness under reduced pressure, the residue is dissolved in water, extracting with cyclohexane, the organic layer is back extracted with water, the combined aqueous layer is added with sodium hydroxide (NaOH), and extracted with chloroform, 5 organic layers are combined and dried over anhydrous sodium sulfate, and rotary evaporated to give a side chain moxifloxacin, pale yellow liquid; (2) in 1000 ml 4-mouth flask equipped with a stirrer, a thermometer, hydrogen chloride tube and hydrochloric acid (HCl) absorption system, adding the crude product before purification of methanol, cooling with stirring when the temperature began to drop to 0 degrees C into concentrated sulfuric acid, passing into dry hydrogen chloride gas, with a salting out crystallization reaction, the reaction mixture temperature is gradually increased to control the reaction temperature below 5 degrees C, stopping reaction with hydrogen chloride for about 6 hours, detecting when the pH is 1, stop hydrogen chloride, continuing cooling and stirring for 1 hour, filtration to obtain crystals substance as a white crystalline side chain double moxifloxacin hydrochloride, the next batch of recycled mother liquor can be applied; (3) in 1000 ml 3-necked flask fitted with a stirrer, and a thermometer adding the obtained product from step (2) and anhydrous methanol, cooling with stirring, when the temperature reaches 0 degrees C, addition of sodium hydroxide, to control the reaction temperature below 5 degrees C and stirring for 5 hours, filtering off solid sodium chloride, and the resulting mother liquor is recovered by distillation at atmospheric pressure before methanol, after distillation under reduced pressure, obtaining the moxifloxacin side chain purification products with chemical purity by GC analysis of 99%.