The etiological typing criteria proposed by the WHO Expert Committee on Diabetes Mellitus (1999) are currently used internationally: 1. Type 1 diabetes mellitus (T1DM): β-cell destruction, often leading to absolute insulin deficiency. 2.Type 2 diabetes mellitus (T2DM): insulin resistance and insulin secretion disorder. 3, other specific types of diabetes mellitus (1) genetic defects in islet β-cell function: maturity-onset diabetes mellitus of the young (MODY): so far there are six subtypes, which are caused by different genetic mutations according to their discovery sequence: MODY1/hepatocyte nuclear factor 4α (HNF-4α), MODY2/Glucose kinase (GCK), MODY3/Hepatocyte nuclear factor 1α (HNF-1α), MODY4/Insulin promoter 1 (IPF1), MODY5/Hepatocyte nuclear factor 1β (HNF-1β), MODY6/Neurogenic differentiation factor 1 (Neuro D1/BETA2). Mitochondrial gene mutation diabetes mellitus (2) Genetic defects in insulin action: type A insulin resistance, leprechaun-looking syndrome, Rabson-Mendenhalll syndrome, adipose atrophy diabetes mellitus, etc. (3) Exocrine diseases of the pancreas: pancreatic inflammation, trauma, surgery or tumor. (4) Endocrine diseases: such as acromegaly, Cushing’s syndrome, pancreatic hyperglycemia, pheochromocytoma, hyperthyroidism, etc. (5) Diabetes caused by drugs or chemicals: such as rodenticide, tobacco acid, glucocorticoids, thyroid hormone, diazoxide, B-adrenergic agonists, thiazides, phenytoin sodium, IFN-A, etc. Most of them can cause hypoglycemic tolerance, etc. 4, gestational diabetes mellitus (GDM): refers to diabetes mellitus that occurs during pregnancy, but does not exclude those who had abnormal glucose tolerance before pregnancy but were not confirmed, patients who are known to be diabetic at the time of pregnancy do not belong to this type. Most of the patients can return to normal after delivery, and nearly 30% of the patients have become diabetic during the 5-10 years follow-up.