The invention provides a composite yacon fruit liquid diet composition and a preparation and use method thereof. The composition comprises raw materials of fruit and vegetables, Chinese medicinal materials and food additives. The fruit and vegetables include yacon fruit, dragon fruit, papaya, lemon and purple sweet potato. The Chinese medicinal materials include beautiful millettia root, dendrobium, cistanche, honeysuckle or safflower, tangerine peel, poria cocos, ginger and licorice. The components of the composition are in scientific proportion, the main components, auxiliary materials and additives are synergic to make a traditional Chinese medicine solution capable of reinforcing muscles and activating collaterals, regulating intestines and stomach and assisting digestion to be blendedinto a liquid beverage rich in dietary fiber and anthocyanin, and a diet combination of drinking water on an empty stomach and then taking aqueous food is adopted to initiate intestinal peristalsis,gut purge, expel toxin, remove harmful bacteria in the intestines and supplement anthocyanins, plant proteins, amino acids, vitamins, mineral trace elements and other nutrients at the same time. The purge gutting effect is quick and good, purge gutting, relaxing and replenishment are all considered, no clear pathological diarrhea or intestinal discomfort such as empty feeling exists, and the quality is table.