Elevated blood sugar in diabetic patients is very dangerous for surgery. If blood sugar is not well controlled before surgery, especially major surgery such as open heart or open abdomen, it is very risky and will increase the mortality rate of the patient and increase the risk of infection of the surgical wound, even if there is no infection, high blood sugar will make the wound heal slowly. On the other hand, surgery itself is a big stress, and if blood sugar is not well controlled, plus the stress has the possibility of leading to diabetic ketoacidosis, or even ketoacidosis coma, it will significantly increase the risk of death of the patient. Therefore, for diabetic patients, it is important to actively control blood sugar before surgery. For general surgery, fasting blood sugar should preferably be below 7.8 mmol/L and postprandial blood sugar below 10 mmol/L. For plastic surgery and eye surgery, etc., which require high wound healing, the blood glucose control target should be stricter, with fasting blood glucose below 6mmol/L and postprandial blood glucose below 8mmol/L, which is conducive to reducing surgical wound infection. Therefore, diabetic patients must actively control their blood sugar before surgery to reduce the risk of surgery.