The invention provides a method for preparing a 2 beta-methyl penicillanate benzhydryl dioxide, which is to prepare the 2 beta-methyl penicillanate benzhydryl dioxide by four-step reactions. In the method, hydrobromic acid and sodium nitrite or cupric bromide serving as a brominating agent and other methods are adopted, especially bromide is generated by using adsorption of anionic resin, and water is a side product, so that the method is safe and environmentally friendly; the resin can be used repeatedly; the reaction molar yield can be remarkably improved, reaching over 75 percent; and dichloromethane, water, little glacial acetic acid, particularly as well as a catalytic amount of concentrated sulfuric acid are used to replace massive glacial acetic acid serving as a solvent, so that massive glacial acetic acid is removed. The method has unique process, stable product quality, mild process condition and easy control, the traditional azidation reaction and ethynylation reaction are eliminated, the production cost is reduced, the environmental pollution is greatly reduced, and no special equipment is required. The method is suitable for industrial generation in scale.