Fasting blood glucose higher than 6.1 mmol/L, 2-hour postprandial blood glucose higher than 7.8 mmol/L, and random blood glucose higher than 11.1 mmol/L can be harmful. Significantly elevated blood glucose in the short term may lead to acute complications such as diabetic ketoacidosis, etc. Poor long-term glycemic control can lead to a variety of chronic complications such as diabetic nephropathy, retinal and cardiovascular pathologies, and neuropathy. Under normal circumstances, the fasting blood glucose range is 3.9-6.1mmol/L, 6.1-7.0,mmol/L belongs to the impaired fasting blood glucose; 1 hour after the meal corresponds to the blood glucose value of 6.7-9.4mmol/L, up to 11.1mmol/L; 2 hours after the meal blood glucose value should be <7.8mmol/L, 7.8-11.1mmol/L belongs to the impaired glucose tolerance. L belongs to impaired glucose tolerance. Blood glucose should be controlled within the normal range to avoid the emergence of various acute and chronic complications, which may cause certain damage to the body. Elevated blood glucose should be diagnosed and treated by a physician in a hospital.