The invention relates to application of a medicine in preparing medicines for treating diabetes mellitus, and belongs to the field of chemical medicines. For solving the technical problem, the invention provides application of the medicine in preparing the medicines for treating the diabetes mellitus. The invention provides the application of the medicines for treating the diabetes mellitus, wherein the formulation of the medicine is a percutaneous absorption preparation; and the medicine comprises the following active ingredients: trivalent V salts of phosphate. Compared with the similar medicines in the market, the medicine has lower cost obviously and reduces the economical burden of the patient; the percutaneous absorption preparation is convenient to use and cannot increase the pain of the patient; and the patient can autonomously take the medicine and stop taking the medicine at any time. Clinical study shows that the medicine does not have obvious toxic or side effects, has obvious effect of treating the diabetes mellitus and is quick to take effect.