Diabetes mellitus (DM) is a group of clinical syndromes caused by the interaction of genetic and environmental factors. It causes a series of metabolic disorders such as sugar, protein, fat, water and electrolytes due to absolute or relative insufficiency of insulin secretion and reduced sensitivity of target tissue cells to insulin. The main clinical hallmark is hyperglycemia, which can cause damage to multiple systems over time. Acute metabolic disorders such as ketoacidosis can occur when the disease is severe or stressful. The clinical type of diabetes can be divided into type 1 diabetes and type 2 diabetes. Type 1 diabetes mostly occurs in young and young adults, and is characterized by rapid onset of symptoms such as polyphagia, polyuria, polydipsia, weight loss, and a tendency to develop ketoacidosis, and must rely on insulin therapy to maintain life. The rate of positive islet cell autoantibodies in blood is high at the beginning of the disease. The oral glucose islet release test shows lower than normal basal insulin levels and a low insulin secretion curve after glucose stimulation, indicating insulin deficiency. Type 2 diabetes can occur at any age, but is mostly seen in middle and old age after the age of 40. Most patients have a slow onset and relatively mild or absent clinical symptoms. There is no tendency to ketoacidosis, but ketoacidosis or hyperosmolar coma can occur under certain triggers. Generally, oral hypoglycemic agents are used to control blood glucose, but when diet and oral hypoglycemic agents are not effective, or when complications and co-morbidities occur, insulin is also needed to control hyperglycemia. Islet cell autoantibodies are often negative. Fasting plasma insulin levels may be normal, mildly decreased or above normal. Insulin response to glucose stimulation may be slightly low, almost normal or above normal, with delayed peak secretion.