The invention discloses a method for preparing 7-alpha-methoxyl-3-deacetyl cefoxitin benzathine salt by reaction of immobilized deacetylases, which comprises the following steps: adding 7-alpha-methoxyl cefoxitin cyclohexylamine salt into purified water, dissolving the salt, adjusting pH, then carrying out enzymolysis, and adjusting pH of enzymolysis liquor after the enzymolysis is finished; adding ethyl acetate into the neutralized enzymolysis liquor, and adding benzathine diacetate into the solution under stirring; and crystallizing the solution, and then throw-drying and drying the crystal to obtain the product. The method reduces links of decoloring and reduced pressure condensing in the prior art, simplifies operation, reduces consumption, reduces production cost, is convenient for operation, avoids using methanol and sodium hydrate, reduces usage amount of acetic acid, reduces pollution, avoids using liquid nitrogen cold source, and does not need subsequent decoloring process. The material cost of the 7-alpha-methoxyl-3-deacetyl cefoxitin benzathine salt can be reduced by 150 Yuan per kilogram, the production period is shortened to one fourth, and the yield of the product can be improved to 73 percent, so the salt has remarkable social and economic effects, and popularization and application prospects.