Normal people have fasting blood sugar of 3.9-6.1mmol/L and 2 hours after meal blood sugar <7.8mmol/L. Usually drinking ordinary plain water, not more than 200mL, has no significant effect on blood sugar; drinking water more than 200mL may cause blood dilution, resulting in mild abnormal blood sugar. If drinking milk, sugar water, honey water and drinks with sugar content, it will affect the blood glucose result. Patients have no deliberate restriction on drinking water during the process of doing pre-meal glucose measurement, post-meal glucose measurement, and glucose tolerance test. Doing the glucose tolerance test, you can drink a small amount in between, and it usually will not cause changes in blood glucose. The glucose tolerance test is mainly to test the reserve function of the body's pancreatic islet cells. Fasting blood glucose is measured first, then 75g of glucose is dissolved in 200mL of liquid, and the blood glucose is tested at 30 minutes, 60 minutes and 120 minutes from the first sip and the curve is depicted. Based on the changes in the curve, it was determined whether abnormal glucose tolerance, as well as diabetes, had occurred. Normal human blood glucose maintains a relatively stable state and is mainly influenced by glucose-raising hormones and glucose-lowering hormones. There are many glucose-raising hormones, but the only glucose-lowering hormone is insulin. When absolute insulin deficiency occurs in the body, it is usually seen in type 1 diabetes, but in type 2 diabetes, due to the long duration of the disease, it is possible that the function of the islet cells may fail after old age due to the prolongation of the disease, and treatment with insulin is required.