If you want to test fasting blood glucose, it is generally required to fast from food and water for 8 hours, especially for patients with initial diagnosis of diabetes must be strictly enforced. In addition, the night before the fasting blood glucose test, do not eat too much sweet and greasy food, need to eat lightly and avoid staying up late. If you want to test postprandial blood glucose, glycated hemoglobin and other related data, drinking water properly before the test at this time has no effect on the value of blood glucose. As long as the amount of water drunk does not exceed 200ml and does not contain brown sugar, white sugar, icing sugar, yellow sugar, honey, etc., or is not a beverage, etc., it is fine. Unless drinking too much water, more than 200ml, may dilute the blood and cause a drop in blood sugar. Diabetic patients should check their blood sugar before and after meals, and the frequency of checking is mainly based on the patient’s blood sugar control. If the blood glucose is well controlled, it can be checked once a week. If the blood glucose is not well controlled or if there is co-infection, the frequency of checking will be more frequent. Patients who have their blood glucose checked will have no effect on their blood glucose as long as they do not drink drinks or sweet water and drink a small amount of water. However, you should not eat food before checking blood sugar, because food has a great influence on blood sugar.