The invention discloses a preparation method of moxifloxacin hydrochloride. The method includes the following steps of making boric acid and acetic anhydride make contact and react for 1 h at a temperature of 85-105 DEG C in protection gas, lowering the temperature to 75-80 DEG C, adding a stable promoter and 1-cyclopropyl-6,7-difluoro-1,4-dihydro-8-methoxy-4-oxo-3-quinolinecarboxylic acid ethyl ester, continuing to conduct stirring for the reaction for 1.5-3 h at a temperature of 75-80 DEG C, conducting monitoring and tracking till the reaction ends, cooling to the room temperature, adding acetonitrile and organic amine to make the mixture react with (S,S)-2,8-diazabicyclo[4.3.0]nonane for 1-2 h at a temperature of 60-70 DEG C, cooling to the room temperature, adding methyl alcohol, dropwise adding concentrated hydrochloric acid at a temperature of 5-10 DEG C, adjusting the pH value to 1-3, conducting stirring for 2 h, cooling to a temperature of -10 DEG C to -5 DEG C, conducting crystallization and suction filtration, conducting washing through cold ethyl alcohol, conducting decompression drying, and obtaining moxifloxacin hydrochloride. The stable promoter is selected from one or more of glycine, serine and threonine. The method is high in yield, simple in operation and aftertreatment and suitable for industrial production.