At present, there are three main methods of insulin injection: 1) multiple subcutaneous insulin injections, which can be done by mealtime plus basal injection or two injections a day. 2) continuous subcutaneous insulin infusion, which is often referred to as insulin pump therapy. 3) new needle-free syringe insulin injection. There are some precautions during insulin injection, the most important one is the occurrence of hypoglycemia during insulin injection. And hypoglycemia may be related to too large a dose of insulin injection or with eating disorders. Mild edema can also occur at the beginning of insulin therapy due to sodium retention, which usually resolves on its own. Some patients may experience blurred vision, which is caused by refractive changes of the lens and often recovers spontaneously within a few weeks. Allergic reactions to insulin may usually manifest as an itchy or hives-like rash at the injection site. Rarely, severe allergic reactions can be treated by changing the insulin preparation, using anti-allergy drugs and glucocorticoids, or desensitization therapy, or in severe cases, stopping or interrupting insulin therapy. Fat malnutrition is mainly manifested as atrophy or hyperplasia of subcutaneous fat at the site of skin injection, which can be recovered naturally after stopping the injection in the area. Therefore, it is necessary to change the injection site frequently during insulin injection to prevent atrophy or hyperplasia of subcutaneous fat.