The action of insulin is mainly to lower blood glucose, but also has the effect of affecting fat and protein metabolism. Insulin increases glucose transmembrane transport, inhibits hepatic glycogenolysis, and promotes protein and fat synthesis, thus exerting a hypoglycemic effect. Insulin can be used for type 1 diabetes mellitus, type 2 diabetes mellitus diet and oral hypoglycemic drugs with poor effect, but also for acute complications such as diabetic ketoacidosis, pregnancy, breastfeeding patients, as well as surgery, infections and other stress hyperglycemia and other conditions. Application of insulin should pay special attention to the occurrence of hypoglycemic reactions, which may include palpitations, hand tremors, sweating, hunger pangs, dizziness, and even coma. There may also be side effects such as weight gain, allergic reactions, redness and hardness on the surface of the insulin injection site. It is contraindicated in patients with hypoglycemia, acute hepatitis, cirrhosis and hemolytic jaundice. Insulin should be used under the guidance of a doctor, do not use it on your own to avoid serious adverse reactions.