The invention discloses a method for preparing sulbactam. The method is characterized by comprising the following steps: reducing dibromine sulbactam from tributyl tin hydride as a reducing agent to prepare sulbactam, namely, adding tributyl tin hydride into a dibromine sulbactam ethyl acetate solution, reacting for hours, subsequently pouring a reaction mixture into water, extracting by using ethyl acetate, combining organic layers, and further washing by using a saturated salt solution; drying the organic layers by using anhydrous magnesium sulfate, and filtering to remove magnesium sulfate; further adding activated carbon, stirring, decoloring and filtering; and washing the filter residues by using ethyl acetate, subsequently putting a mother liquid into a rotating evaporator, performing vacuum evaporation by using a water bath, stopping evaporating when crystals are separated out, cooling down, performing suction filtration, and drying in vacuum so as to obtain white sulbactam crystals. The method is gentle in reaction conditions, free of flammable, combustible and high-toxicity reagents, high in yield when being prepared with a preparation of a document, is an economic and practical synthesis method, and is applicable to large-scale industrial production.