The invention discloses an application of isoflavone which has substituent in the two intermediate rings and is taken as an animal feed additive, an animal oral dose or an animal water mixture agent. The isoflavone which has substituent in the two intermediate rings is taken as the animal feed additive used in the feed of animals such as pig, poultry, aquatic livestock, ruminant, and the like, thus promoting animal growth and improving feed utilization, animal immunity and reproductive property. The isoflavone can be used for replacing antibiotics used in feed or other feed additives which promote animal growth so as to eliminate the antibiotic residue in cultured animal products, to produce safe cultured animal products with good quality and reduce feed or culture cost. The isoflavone has high biological activity, stable quality, low use cost, no residue, no toxicity, no mutagenesis, carcinogenesis or teratogenesis, so the isoflavone is a green, safe, high efficient and environment-friendly feed additive.