Insulin is suitable for patients with type 1 diabetes mellitus and type 2 diabetes mellitus, patients with diabetes mellitus combined with acute or chronic complications (such as infections, diabetic ketoacidosis, diabetic nephropathy, hepatic insufficiency, etc.), patients with surgeries, pregnancies and deliveries, patients with new-onset diabetes mellitus that is difficult to differentiate from type 1 diabetes mellitus, as well as patients with certain special types of diabetes mellitus. 1. Timing of starting treatment for patients with new-onset diabetes mellitus: ① newly diagnosed type 2 diabetes mellitus with obvious hyperglycemia symptoms, ketosis or ketoacidosis; ② difficult to differentiate from type 1 diabetes mellitus. 2. Timing of starting treatment for patients with diagnosed diabetes mellitus under treatment: ① After 3 months of combined treatment with lifestyle intervention and oral hypoglycemic agents, blood glucose still fails to reach the control target; ② the occurrence of significant weight loss without obvious triggers; ③ perioperative period, pregnancy, and co-infections; ④ persistence of glucose ≥ 10.0 mmol / L during hospitalization. Patients who need insulin therapy should use it in a standardized way under the guidance of professional doctors, and should not apply it blindly on their own.