The invention relates to a pharmaceutical composition for diabetic nephropathy and its preparation, and the application in preparing of medicine for diabetic nephropathy. The pharmaceutical composition is made up of at least one of 7-hydroxycoumarin and 7-hydroxy-6-methoxycoumarin as active ingredient, and the weight percentage of active ingredient is 0.1-99.5%. Moreover, the pharmaceutical composition is mainly used for the prevention and cure of diabetic nephropathy. For the abundant material, remarkable effect on prevention and cure for diabetic nephropathy and convenience for use, it will be a new facultative drug for patients.
