Elevated blood sugar in diabetic patients can be very harmful to surgery. If surgery is done without good blood sugar control, especially major surgery such as open heart or open abdomen, it is very risky and will increase the mortality rate of the patient, increase the risk of infection of the surgical wound, and even if there is no infection, the high blood sugar will make the wound healing slow. On the other hand, surgery itself is a big stress, if the blood glucose is not well controlled, plus the stress has the potential to cause diabetic ketoacidosis, or even ketoacidotic coma, which will significantly increase the risk of death for the patient. Therefore, for diabetic patients, it is necessary to actively control blood glucose before surgery. For general surgery, fasting blood glucose should preferably be below 7.8 mmol/L, and postprandial blood glucose should be below 10 mmol/L. For plastic surgery and eye surgery, etc., which require high wound healing, the goal of glycemic control should be stricter, with fasting blood glucose below 6mmol/L and postprandial blood glucose below 8mmol/L, which is conducive to minimizing surgical wound infection. Therefore, diabetic patients must actively control their blood glucose before surgery to reduce the risk of surgery.