The invention discloses a dendrobium officinale composition and a preparation method and application thereof.The dendrobium officinale composition is prepared from, by weight, 10-50 parts of dendrobium officinale and 5-30 parts of radix asparagi, the medicine components are mixed and smashed, a certain amount of water is added, the medicine components are soaked for a period of time and subjected to reflux extraction, an extracting solution is filtered, filtrate is subjected to vacuum concentration, and a traditional Chinese medicine composition extract is obtained. The composition disclosed by the invention has a relatively good prevention and treatment effect on ulcerative colitis, and can be used for remarkably reducing the disease activity score (DAI score) of a mouse with ulcerative colitis, increasing the colon length, improving the histological lesions such as colonic mucosa injury, inflammatory cell infiltration, goblet cell and mucus reduction and the like, and preventing and treating the ulcerative colitis. One of the ways for preventing and treating ulcerative colitis is to increase the abundance of UCG-007 bacteria in intestinal flora. The traditional Chinese medicine composition has the characteristics of simple formula and exact curative effect, and has better effect, lower cost and good market development and application prospects compared with single use of dendrobium officinale.