The invention discloses a feed additive capable of resisting heat stress and relieving oxidative stress injuries and used for broiler chickens. The feed additive is prepared from the following raw materials in parts by mass: 20-30 parts of compound Chinese herbal medicine extract, 15-20 parts of a yeast culture, 5-10 parts of alpha-ketoglutaric acid, 5-10 parts of glycine betaine, 2-4 parts of sodium hydrogen carbonate, 4-8 parts of ammonium chloride, 3-5 parts of magnesium sulfate and 2-3 parts of chromium picolinate, wherein the compound Chinese herbal medicines comprise garden burnet roots, dandelions, indigowoad roots, spina date seeds, Chinese fevervine herb, herb of shorthorned epimedium, astragalus membranaceus, Chinese angelica, common andrographis herb and liquorice roots. With the adoption of a scientific proportion of a plurality of raw materials with different types, the '1+1>2' synergistic effect is realized; the product has a remarkable effect, the heat stress resisting capability of the broiler chickens under a high-temperature condition can be remarkably improved and the oxidative stress injuries can be relieved; the nutrition digestion rate is improved, the growth is promoted and the feed / gain ratio is reduced; and the feed additive is safe and convenient to use, does not have the problems of drug residues, drug resistance and the like, and has a wide market prospect.