High fasting blood glucose in the morning may be caused by eating too much the night before, Sumuje phenomenon, dawn phenomenon and so on. 1. Eating too much the night before: blood sugar is greatly affected by diet, if you eat too many carbohydrates or eat a lot of high-calorie food the night before will make the body’s blood sugar fluctuations, eat and then go to sleep, which will lead to the next day’s high fasting blood sugar. 2. Sumuje Phenomenon: It is the reactive hyperglycemia after hypoglycemia. Some patients may have hypoglycemia at 1~3 a.m. The body will have a self-regulation and protection mechanism to correct the hypoglycemic reaction, such as over secretion of glucagon, including adrenocorticotropic hormone and glucagon, and the fasting blood glucose will be elevated the next morning. 3. Dawn phenomenon: It refers to a state of early morning hyperglycemia caused by increased secretion of glucagon in diabetic patients at dawn when their blood glucose control is still good and stable at night without hypoglycemia. High fasting blood glucose in the morning can be determined by multiple measurements of nighttime blood glucose to determine the cause of the disease, and it is recommended to consult a doctor in a timely manner, under the guidance of the doctor to carry out the relevant examinations and treatments.