The invention discloses a feed additive for weaned pigs, capable of controlling respiratory diseases and improving immunity. The feed additive comprises the following raw materials by mass: a composite Chinese herbal medicine extract, amino acid chelate trace elements, vitamin C, folic acid, biotin, acidic pectinase, neutral protease, amylase, xylanase, phytase, cellulase, taurine, cysteamine, sodium butyrate and a microecological preparation, wherein composite Chinese herbal medicines comprise forsythia suspensa, honeysuckles, Chinese thorowax, acanthopanax bark, platycodon roots, field thistle herbs, nutgrass galingale rhizomes, folium isatidis, astragalus membranaceus, licorice roots, radix isatidis, mint, radix codonopsis, atractylodes rhizomes and glossy privet fruits. According to the feed additive disclosed by the invention, the composite Chinese herbal medicine extract, the amino acid chelate trace elements, the multizyme preparation, the microecological preparation and the like are in scientific compounding, so that the effect of synergistic reaction that various Chinese herbal medicines are compounded to have better effects than separate Chinese herbal medicine, is achieved, the products are notable in effects, and the respiratory disease of the weaned pigs can be effectively controlled. The feed additive is safe and convenient to use, the problems of drug residues, drug tolerance and the like are solved, and the feed additive has broad market prospects.