1.Introduction to glucose tolerance test: Glucose tolerance test, also known as glucose tolerance test, is a laboratory test for the diagnosis of diabetes mellitus. The former is called IVGTT and the latter is called OGTT. IVGTT is only used to evaluate glucose utilization as a means of clinical research, or in special patients after gastrectomy, malabsorption syndrome, etc. OGTT is the most common clinical test. 2, indications for glucose tolerance test: (1) clinical suspicion of diabetes mellitus, can not be determined by blood glucose test results alone. (2) Diabetes mellitus has been diagnosed, need to do a comprehensive understanding of the patient’s peak glucose secretion, insulin secretion function, C peptide, etc. (3) Other causes of diabetes identification, such as renal diabetes, trophoblastic diabetes, etc. 3, the method of glucose tolerance test (1) test before the daily carbohydrate intake of at least 150g, with normal physical activity for at least 3 days. (2) Overnight fasting 10-14 hours. (3) Prohibit alcohol, coffee and tea before the test, and maintain emotional stability. (4) Fasting blood should be drawn before 8:30 a.m., and then drink 250-300 ml of water containing 75 g of glucose within 5 minutes. (If fasting blood glucose > 15.0 mmol/L or type 1 diabetes with ketosis tendency, replace with 100 grams of flour buns and finish within 10-15 minutes). (5) Blood was drawn once immediately, 1 hour, 2 hours and 3 hours after drinking sugar water or eating buns, respectively, to measure blood glucose value and insulin level, etc. 4. Clinical significance of glucose tolerance test (1) Normal value: fasting 3.9-6.1mmol/L, 1 hour blood glucose rise to peak <11.1mmol/L, 2 hours fall <7.8mmol/L, 3 hours fall in fasting value. (2) Confirmation of diabetes mellitus. Fasting blood glucose ≥7.0mmol/L or postprandial blood glucose ≥11.1mmol/L. (3) Understand the range of blood glucose fluctuation and analyze the degree of diabetes stability. The fluctuation range of fasting blood glucose in normal people is 3.9-6.1mmol/L. The smaller the difference between fasting blood glucose and 3 hours postprandial blood glucose value in diabetic patients, the more stable it is, and vice versa.