Preprandial blood glucose is fasting blood glucose. Preprandial blood glucose 6.3mmol/L is an abnormal condition, with high blood glucose and the possibility of impaired fasting blood glucose, and patients are advised to review their blood glucose in detail. If there is postprandial blood sugar ≥11.1mmol/L in addition to preprandial blood sugar 6.3mmol/L, one should be alert to diabetes. Normal people have pre-meal blood glucose of 3.9-6.1mmol/L. If a woman in pregnancy has pre-meal blood glucose of 6.3mmol/L, she can be tentatively diagnosed with gestational diabetes. In addition, if one is over 40 years old and has a history of obesity, family diabetes, and suffers from hypertension, coronary heart disease, hyperlipidemia, hyperuricemia and other diseases in itself, finding a pre-meal glucose of 6.3mmol/L, one should also pay high attention and be alert to the risk of developing diabetes. However, there are exceptions. If a diabetic patient has a pre-meal glucose of 6.3mmol/L after diet, exercise and medication, it can be considered normal. In addition, it is necessary to pay attention to the patient’s 2-hour postprandial blood sugar, and it is best to control the 2-hour postprandial blood sugar within 8.5mmol/L, because only when the diabetic patient’s blood sugar reaches the standard can the occurrence of various complications be reduced, including diabetic ketoacidosis, lung infection, urinary tract infection, skin infection, etc.