The diagnosis of diabetes mellitus includes the following three aspects: First, the patient has typical symptoms of diabetes mellitus, such as drinking more, eating more, urinating more, accompanied by weight loss, checking blood sugar, fasting blood sugar > 7.0mmol/L, postprandial blood sugar, especially refers to two hours after blood sugar > 11.0mmol/L, can be considered as diabetes mellitus. Second, the patient does not have typical clinical manifestations, but perfect the screening test of glucose tolerance, the patient’s fasting blood glucose > 7.0mmol/L, two hours after meal blood glucose > 11.0mmol/L, repeated twice blood glucose are above results, can be diagnosed as diabetes mellitus. Third, the patient’s random blood glucose ≥ 11.1mmol/L, and accompanied by the typical symptoms of three more and one less, that is, drinking more, eating more and urinating more and losing weight, also can be diagnosed as diabetes. The above three ways are the three main ways to diagnose diabetes.