The general diagnostic criteria of diabetes mellitus are still used in the WHO diagnostic criteria in 1999. The criteria for confirming the diagnosis of type 2 diabetes in Chinese clinical guidelines are briefly described as follows: 1. With typical symptoms, fasting blood glucose ≥7.0mmol/L or postprandial blood glucose ≥11.1mmol/L can confirm the diagnosis of diabetes. 2.No typical symptoms, only fasting blood sugar ≥7.0mmol/L or postprandial blood sugar ≥11.1mmol/L should be repeated once more, still reach the above value, can be diagnosed as diabetes. 3, no typical symptoms, only fasting blood sugar ≥ 7.0mmol/L or postprandial blood sugar ≥ 11.1mmol/L, glucose tolerance test 2 hours blood sugar ≥ 11.1mmol/L can be diagnosed as diabetes mellitus. If the glucose tolerance test 2-hour blood sugar is between 7.8-11.1mmol/l, the diagnosis is glucose tolerance reduction. If fasting blood glucose is 6.1-7.0mmol/L as impaired fasting blood glucose. In addition, during pregnancy, the diagnosis of diabetes is more stringent, and it is generally considered that the diagnosis is confirmed by exceeding one of the criteria of fasting glucose > 5.1 mmol/L, 60 minutes > 10.0 mmol/L and 120 minutes > 8.5 mmol/L. At present, foreign guidelines have begun to gradually add the level of glycated hemoglobin to the diagnostic criteria, but it has not been adopted in China for various reasons. These diagnostic criteria are very complex, and the specificity of whether someone has diabetes depends on the specific situation and blood glucose level, and if necessary, the relevant glucose tolerance test is performed to confirm the diagnosis.