The invention discloses a feed additive capable of preventing and treating a chronic aleutian disease of minks and a preparation method of the feed additive. The feed additive is prepared from the following components of enteromorpha, seeds of coral peatree, black sesame seeds, kelp, clamworm powder, fish scales, olive oil, herb of sibirica walking fern, radix rubiae, roots of snow of June, kochia scoparia seedlings, largehead atractylodes rhizomes, corn stigma, fennel fruits, radix linderae, bauhinia variegate roots, bark, leaves and flowers, pummelo seeds, russula virescens, roots or stem of smoothfruit ventilago, roots of silverweed cinquefoil, radix curcumae, ginseng, radix polygoni multiflori and licorice roots. The feed additive disclosed by the invention does not contain antibiotics, is non-toxic and harmless to the minks, and is convenient to use; medicines can exert effects quickly, the feed additive has a good treatment effect on the minks suffering from the chronic aleutian disease, the immunity of the minks is strengthened, and increase of economic benefits of breeding households is facilitated.