The invention discloses a composition for promoting growth of weaned piglets and a preparation method and application of the composition, and relates to the technical field of piglet feed. Specifically, raw materials of the composition comprise main ingredients, and the main ingredients is prepared from the following components in parts by weight: 20-50 parts of Chinese yam, 20-50 parts of gorgoneuryale seed, 20-50 parts of lotus seed, 20-50 parts of fructus amomi, 20-50 parts of fried semen coicis, 20-50 parts of fried white hyacinth bean, 20-50 parts of tangerine peel, 15-30 parts of caramel malt, 15-30 parts of poria cocos, 15-30 parts of medicated leaven, 15-30 parts of endothelium corneum gigeriae galli, 15-30 parts of bark of ash, 10-25 parts of radix glehniae and 10-25 parts of roasted rhizoma atractylodis macrocephalae. The composition can replace traditional western medicine antibiotics or hormonal medicine as growth-promoting feed additives, and further has the effects of enhancement of qi tonifying and spleen tonifying and growth-promoting While the immunity and disease resistance of the piglets are ensured, the investment in breeding is reduced, and economic benefits are improved.