The invention relates to the field of medicine and discloses the medical purpose of puerarin. The puerarin has an inhibition function on alpha-glucuronide and alpha-amylase, and the inhibition effect of the puerarin is 1-3 times of that of acarbose, therefore, the puerarin can be used for preparing an alpha-glucuronide inhibitor, an alpha-amylase inhibitor and medicaments for treating diabetes mellitus. When applied to preparing the alpha-glucuronide inhibitor, the alpha-amylase inhibitor and the medicaments for treating the diabetes mellitus, the puerarin has the advantages of stable properties and good safety; and the puerarin has high content in plants, simple extraction process, easy obtainment of source, economic benefit and safety, thereby having great generalization and application value.