Diabetes mellitus is a heterogeneous group of metabolic diseases characterized by chronic hyperglycemia and is associated with genetic, autoimmune and environmental factors. It causes abnormal metabolism of sugars, proteins and fats due to defective insulin secretion and/or insulin action. The long-term course of the disease can cause multi-system damage, leading to chronic complications of blood vessels, heart, nerves, kidneys, eyes and other tissues and organs, and in severe cases, acute complications such as diabetic ketoacidosis and diabetic hyperglycemic hyperosmolar state. The typology of diabetes includes the following types: Type 1 diabetes: characterized by destruction of pancreatic islet B cells and/or severe insulin secretion disorder (absolute insulin deficiency), insulin and C-peptide levels are significantly reduced or even undetectable, with a tendency toward ketoacidosis, and patients usually require insulin to stay alive. Type 2 diabetes: Decreased insulin secretion (or relative decrease) caused by the decrease of insulin’s ability to regulate glucose metabolism (insulin resistance) along with pancreatic beta cell deficiency. hyperglycemia, hyperthyroidism, and so on, all belong to secondary diabetes mellitus. In addition, some medications used to treat other diseases can also cause elevated blood glucose, such as glycocorticoids, niacin, thiazide diuretics, etc., all of which may lead to secondary elevation of blood glucose. Gestational diabetes: refers to abnormal glucose metabolism that occurs during pregnancy, including both diabetes combined with pregnancy and gestational diabetes. In the former case, diabetes is present first and then pregnancy, while in the latter case, abnormal blood glucose is first detected after pregnancy and is associated with specific hormone levels during pregnancy, some of which can recover after delivery, while others develop lifelong diabetes. Therefore, diabetes is not an isolated disease, but a group of diseases caused by many factors and characterized by chronic elevation of blood glucose in common.