The invention discloses a preparation method of florfenicol. The method comprises the following steps of: (1) putting (4S,5R)-2-dichloromethyl-5-(4-methylsulfonyl phenyl)-4-methyl fluoride-1,3-oxazoline, a catalyst and a solvent into a reaction kettle, wherein the mass volume ratio of the (4S,5R)-2-dichloromethyl-5-(4-methylsulfonyl phenyl)-4-methyl fluoride-1,3-oxazoline to the solvent is 1:(2-3), the catalyst is any one of iodine, cupric chloride dehydrate or titanium tetrachloride, and the solvent is the mixture of methanol, ethanol and water; (3) heating a mixed solution obtained in the step (1) for reflowing, reacting, and cooling to the room temperature; and (3) performing suction filtration on the mixed solution which is cooled to the room temperature in the step (2), washing a filter cake once with ethanol, performing suction filtration, recovering an ethanol mother liquor, and drying the filter cake to obtain florfenicol. In the method, the florfenicol is obtained under a mild and approximately neutral reaction condition, so that the preparation cost is reduced, and the yield is increased.