Many people have a misconception that high blood sugar is diabetes. In fact, there are many causes of transient blood sugar elevation, such as an occasional excessive intake of sugar or starch, sudden emotional fluctuations, severe lack of sleep, and an increase in adrenaline due to too cold or hot weather, so an occasional high blood sugar does not necessarily mean diabetes. The reference value of fasting blood glucose for normal people is 3.9 to 6.1mmol/L, and the blood glucose two hours after meal should be less than 7.8mmol/L. To detect blood glucose over this range is considered high blood glucose. And the diagnostic criteria of diabetes are: blood glucose ≥ 11.1mmol/L at any time or fasting blood glucose ≥ 7.0mmol/L or blood glucose ≥ 11.1mmol/L two hours after glucose load, for asymptomatic patients, there must be two blood glucose abnormalities to make the diagnosis. For those with blood glucose higher than the normal range but not meeting the diagnostic criteria for diabetes, an oral glucose tolerance test (OGTT) is required to clarify the diagnosis. Thus, it can be seen that high blood sugar may not necessarily mean diabetes. However, we should pay attention to blood glucose in general and prevent it before it becomes a disease. We can lower blood glucose and live a healthy life by drinking more water, exercising properly, controlling diet, regular work and rest, and paying attention to balanced nutritional intake to prevent the occurrence of diabetes.