The invention relates to a purifying method of interferon. The method comprises the following steps of a. performing fermentation culture by selecting engineering bacteria as bacterial strains; b. separating and washing inclusion bodies of the bacterial strains obtained from the fermentation culture to obtain refined inclusion bodies; c. performing renaturation on the refined inclusion bodies to obtain a renaturation preoduct; d. performing anionic column chromatography treatment on the renaturation product to obtain an anionic column chromatography product; d. performing cation column chromatography treatment on the anionic column chromatography product to obtain a cation column chromatography product; and f. processing the cation column chromatography product by using a reverse phase packing column chromatography, and performing desalinizing treatment to obtain the interferon.