The invention discloses dehumidification weight reducing oral liquid and a preparation method thereof. The dehumidification weight reducing oral liquid comprises, by weight, 3-20 parts of tangerine peel, 6-20 parts of Indian bread, 6-20 parts of seeds of Asiatic plantain, 6-20 parts of ginseng roots, 10-60 parts of fried rhizome of largehead atractylodes, 6-30 parts of fried rhizome of common yams, 6-20 parts of tangshen roots, 6-50 parts of astragali radix, 3-15 parts of agaric, 3-15 parts of rhizome of ternate pinellia, 3-15 parts of roots of ural licorice, 6-25 parts of fried coix seeds, 6-30 parts of seeds of gordon euryale, 6-50 parts of radix astragali preparata, 6-30 parts of parched hawthorn fruits, 6-30 parts of parched medicated leaven, 6-30 parts of dark malt and 3-15 parts of rhizome of common ginger. The dehumidification weight reducing oral liquid is applicable to obese patients with damp abundance due to splenic asthenia, phlegm-damp, qi-insufficiency constitution and the like, has the functions of tonifying middle-Jiao and Qi, clearing damp, promoting diuresis, drying damp and eliminating phlegm by the aid of traditional Chinese medicines to enhance body gastrointestinal metabolism functions and achieves weight reducing effects. The dehumidification weight reducing oral liquid has the advantages that dieting, strenuous exercise and purgatives are omitted, and the weight reducing effects are good.