Dawn phenomenon can be considered if nighttime blood glucose is not lower than 6.0 mmol/L and fasting hyperglycemia occurs this morning. Dawn phenomenon is a normal nighttime blood glucose and early morning fasting hyperglycemia in diabetic patients receiving oral hypoglycemic drugs or insulin therapy. Dawn phenomenon is the result of elevated secretion of various insulin antagonist hormones, such as glucocorticoids, catecholamines, glucagon, thyroid hormones, etc., which cause a transient increase in blood glucose in the early morning. Dawn phenomenon is characterized by normal blood glucose at night and elevated fasting blood glucose. Therefore, patients suspected of dawn phenomenon need to monitor blood glucose dynamically at 0:00 and 2:00 at night to exclude hypoglycemic hyperglycemia caused by night hypoglycemia, and if necessary, do dynamic blood glucose monitoring to exclude hypoglycemia at night and hyperglycemia caused by insufficient insulin action.