The invention discloses a method for preparing an amprenavir midbody serving as anti-AIDS medicine. According to the method, L-phenylalanine serves as raw materials, tertiary butyl is adopted for protection and esterification, CuCl<2>/DMF cholro and sodium borohydride serve as reducing agents, binaphthol phosphamidon compounds obtained through complexation of ruthenium trichloride and (+)-B-chlorodiisopinocampherylborane serve as catalysts, and a target product, namely (2R, 3S)-1, 2-epoxy group-3- amine tert-butoxide group-4-phenylbutane, is synthesized in an efficient and asymmetrical mode. By means of the method, the binaphthol phosphamidon compounds obtained through complexation of ruthenium trichloride and (+)-B-chlorodiisopinocampherylborane serve as the catalysts, the proportion of erythro form structures in the reduction reaction product is greatly raised, waste of raw materials is avoided, meanwhile, the separation cost is decreased, and the method is economic, safe and more suitable for large-scale industrial production.