Preparation method of high-purity dutasteride

The invention discloses a preparation method of high-purity dutasteride. Acetonitrile residues in the dutasteride are not more than 0.04%, formula V impurity residues in the dutasteride are not more than 0.02%, and the total impurities of the dutasteride is not more than 0.15%. The preparation method includes synthesizing and refining crude dutasteride. By the preparation method which has obvious advantages as compared with the prior art, the acetonitrile residues in the finished-product dutasteride are reduced effectively, and the generation of formula V compound impurities can be avoided effectively.