Possible reasons for high fasting blood glucose and low postprandial blood glucose include dawn phenomenon, Sumuje phenomenon, improper application of drugs, improper diet and exercise. 1. Dawn phenomenon: early in the morning, the body’s growth hormone, glucocorticoid and other glucagon secretion increases, while the body has only insulin, a glucagon, so it may lead to fasting blood sugar. 2. Sumuje phenomenon: hypoglycemia occurs at night, which in turn causes a rebound increase in fasting blood glucose. 3. Improperly applied drugs: Insufficient basal insulin or glucose-lowering drugs to reduce fasting blood glucose applied to diabetic patients may lead to high fasting blood glucose; excessive application of short-acting (or pre-mixed) insulin or oral hypoglycemic drugs to reduce postprandial blood glucose may lead to low postprandial blood glucose. 4. Improper diet and exercise: If you eat less and exercise more, it may lead to low blood glucose after meal. Patients with high fasting blood glucose and low postprandial blood glucose should go to the hospital to find out the cause and be treated under the guidance of the doctor.