The invention discloses a Chinese patent drug for treating diabetes and a preparation method thereof, relating to the technical field of traditional Chinese medicine. The Chinese patent drug comprises the following effective ingredients in parts by weight: 50-70 parts of grapestone, 50-70 parts of white tea, 50-70 parts of lucid ganoderma, 50-70 parts of ginseng, 50-70 parts of hawthorn, 3-5 parts of the root of red-rooted salvia, 10-15 parts of rhizoma atractylodis, 10-15 parts of vine root, 10-15 parts of folium mori, 20-25 parts of bitter gourd, 10-15 parts of Cyclocarya paliurus, 10-20 parts of garlic, 20-30 parts of pumpkin powder, 10-20 parts of persimmon tree leaf, 10-20 parts of corn stigma, 5-20 parts of pomegranate, 5-15 parts of semen coicis, 10-15 parts of Coptis chinensis, 10-15 parts of lophatherum gracile, 5-10 parts of turmeric and 10-15 parts of eucommia bark. The Chinese patent drug prepared with the preparation method has the efficacy on lowering cholesterol, lowering blood fat, lowering blood pressure, lowering blood sugar, improving internal fat metabolism, enhancing organism immunity functions and the like and can be used for treating diabetes.