Type 2 diabetes mellitus is caused by endogenous insulin secretion defect or insulin resistance. To determine whether it is type 2 diabetes mellitus, we can comprehensively judge from the aspects of blood glucose, age of onset, mode of onset, and whether it is prone to ketoacidosis. Type 2 diabetes is caused by endogenous insulin secretion defects or insulin resistance. The disease has an insidious onset and may have no obvious clinical manifestations, or it may have symptoms such as polydipsia, polyphagia, polyuria, and so on. To diagnose type 2 diabetes, fasting blood glucose should be greater than or equal to 7mmol/L or glucose tolerance test two-hour blood glucose greater than or equal to 11.1mmol/L, and have typical diabetes symptoms. Moreover, type 2 diabetes usually starts at an age greater than 40 years, starts slowly and insidiously, symptoms are not very obvious, it is often combined with obesity, there may be insulin resistance, and there is a delay in insulin peaks. Patients who are suspected of having type 2 diabetes or who are not sure which type of diabetes they have can go to the hospital and ask the doctor to make a comprehensive judgment in conjunction with their own situation.