The invention discloses a pharmaceutical composition for treating diabetic nephropathy, a preparation method thereof, and application in the preparation of a drug for treating diabetic complications. The pharmaceutical composition consists of one or two of 7-hydroxycoumarin or 7-hydroxy-6-methoxy coumarin as active ingredients and a conventional drug carrier, and the content of weight percentage of the active ingredients is 0.1-99.5%. The pharmaceutical composition is mainly used in the preparation of the drug for treating diabetic nephropathy. The pharmaceutical composition has rich source of raw materials, obvious preventive effect for diabetic nephropathy, and convenient use, and provides a novel drug candidate for treatment.
