The invention relates to application of cortex moutan extract in preparation of a hypoglycaemic agent and aims at solving the problem of preparation of the hypoglycaemic agent. According to the technical scheme, the cortex moutan extract is obtained by the following steps: taking a cortex moutan medicinal material, smashing cortex moutan into coarse powder, adding NaCl aqueous solution, soaking, then distilling and extracting, collecting distillate, cooling to room temperature, refrigerating, after cortex moutan phenol crystals are separated out, filtering to obtain primary crystals; adding NaCl into filtrate, distilling again, collecting distillate with the volume of being three times that of the filtrate, refrigerating, staying overnight, filtering to obtain secondary crystals, putting the primary crystals and the secondary crystals together, and drying under reduced pressure, so that the cortex moutan extract is obtained, wherein cortex moutan phenol mass content is more than 80%. Raw materials are available, a preparation method is simple, the obtained cortex moutan extract is effective and can be used for preparing the hypoglycaemic agent, so that the application of the cortex moutan extract in the preparation of the hypoglycaemic agent is realized; meanwhile, the cortex moutan extract also can be used for further realizing preparation of a drug used for treating diabetes, so that medicinal value of cortex moutan is increased and a new application of the cortex moutan is developed.