The invention relates to a feed additive for treating the bacterial enteritis disease of phractocephalus hemioliopterus, as well as a preparation method for the feed additive. The feed additive is prepared from the following components in parts by mass: 40 to 48 parts of flos puerariae, 21 to 27 parts of Huangpao, 24 to 28 parts of houttuynia cordata, 30 to 35 parts of rhizoma phragmitis, 8 to 12 parts of endothelium corneum gigeriae galli, 3 to 5 parts of tangerine peel, 12 to 17 parts of dandelions, 17 to 25 parts of opuntia dillenii haw, 14 to 19 parts of folium isatidis, 18 to 25 parts of onions, 11 to 15 parts of mint, 14 to 20 parts of portulaca oleracea, 13 to 18 parts of tree peony barks, 2 to 3 parts of pu-erh tea, 15 to 20 parts of fructus cnidii, 11 to 16 parts of pine nuts, 15 to 21 parts of lithospermum purpurocaeruleum, 16 to 22 parts of Chinese pulsatilla roots, 17 to 22 parts of persicaria orientalis, 18 to 25 parts of cortex phellodendri, 9 to 14 parts of eucommia ulmoides oliv, 15 to 21 parts of barley and the like. The feed additive is environment-friendly, and can be used for effectively treating the bacterial enteritis disease of the phractocephalus hemioliopterus.