The invention relates to a preparation method of an oseltamivir enantiomer as shown in a formula I. The method includes the steps: attacking epoxy from back surface by a compound II through sodium azide under the action of ammonium chloride to obtain a compound III; catalyzing the compound III to obtain a compound IV; treating the compound IV under the actions of triethyl silicane and titanium tetrachloride to obtain a compound V; reducing azide by the compound V under the action of triphenylphosphine, and performing loop closing on the compound V and adjacent hydroxyls to obtain a compound VI; attacking cyclamine to open rings from back surface by the compound VI through sodium azide under the action of ammonium chloride, simultaneously overturning a configuration, and performing acetylation by the aid of acetic anhydride to obtain a compound VII; performing Staudinger reaction on the compound VII under the action of triphenylphosphine to reduce the azide into amino to obtain the oseltamivir enantiomer as shown in the formula I. The preparation method of the oseltamivir enantiomer has significance for quality research and quality control of oseltamivir phosphate.