Fasting blood glucose 12 mmol/L is high blood glucose, it is recommended to go to the hospital in a timely manner, further glucose tolerance test under the guidance of the physician, clear diagnosis and then appropriate treatment. The diagnostic criteria for diabetes mellitus are fasting blood glucose ≥7.0 mmol/L, 2-hour postprandial blood glucose ≥11.1 mmol/L, and random blood glucose ≥11.1 mmol/L with the typical “three more and one less” symptoms of diabetes mellitus. Fasting blood glucose 12 mmol/L can be clearly diagnosed as diabetes mellitus when the elevation of blood glucose caused by stress conditions is excluded and the patient’s postprandial blood glucose value is abnormal, accompanied by symptoms such as excessive drinking, excessive urination, excessive food and weight loss. If diagnosed with diabetes mellitus, the patient should follow the doctor’s instructions to standardize the treatment with glucose-lowering drugs such as insulin injections, oral acarbose, glimepiride, etc., which, together with strict dietary and exercise therapies, can lower the blood glucose to the normal range. At the same time, patients are advised to monitor their blood glucose regularly, and go to the hospital in time if they have abnormal blood glucose values.