Method for preparing repaglinide

The invention relates to a preparation method of a drug for treating diabetes mellitus, that is, repaglinide. The preparation method comprises the following steps: a (S) type compound as shown in formula (II) and a compound as shown in formula (III) are subject to an amidation reaction in the presence of a condensing agent to generate a (S) type compound as shown in formula (IV); R2 radical is removed from the (S) type compound of the formula (IV) in the presence of alkali, and R1 radical is removed in the presence of acid. The (S) type compounds as shown in the formula (II), the formula (III) and the formula (IV), and the R1 radical and the R2 radical are defined in the specification. In the preparation method, the introduction of the R1 radical and deprotection improvement shorten the reaction time, increase the yield and enhance safety, thus the method is more suitable for industrialized production.