Abstract: The present disclosure provides a method for preparing a pyrazine compound of formula (I). In the present disclosure, 3-hydroxyl-6-bromopyrazine-2-amide is subjected to a reaction in the presence of phosphorus oxychloride and DIEA, during which adding an organic inorganic chloride makes the content of impurities greatly decreased, thereby obtaining 3,6-dichloropyrazine-2-carbonitrile with high-purity. 3,6-dichloropyrazine-2-carbonitrile prepared in the present disclosure is high in purity, low in production cost and suitable for industrial scale-up production and is very helpful for follow-on production of favipiravir API.