Diabetes mellitus is a metabolic disease characterized by hyperglycemia due to defective insulin secretion or impairment of its biological action. It is one of the oldest diseases ever discovered by man. It has been known to mankind for at least 3,500 years since the beginning of its existence in definite historical records. With the improvement of people’s living standard, the aging of the population and the increase of the incidence of obesity, the incidence of diabetes is increasing year by year, becoming an increasingly serious public health problem that is spreading worldwide. The prevalence of diabetes in China has reached 2%, with 40 million people diagnosed with diabetes, and is increasing at a rate of 1 million per year. The traditional treatment model for type 2 diabetes mellitus (T2DM) is mainly based on medical therapy, including diet control, exercise, oral hypoglycemic drugs and insulin injections, however, none of these approaches can satisfactorily control the progression of diabetes mellitus and its complications. There is a strong relationship between diabetes and obesity. Sixty-five percent of the diabetic population is overweight or obese, and 70-80% of diabetics over the age of 40 have a history of obesity. Conversely, the incidence of diabetes in obese people is four times higher than in non-obese people. Patients with combined obesity not only have a poorer prognosis than non-obese patients, but also have a 2.5 times higher mortality rate. The fundamental reason why obese people are prone to diabetes is that there is a special pathological state of insulin resistance in their bodies, that is, the cells are resistant to the action of insulin, and it is difficult for glucose in the blood to enter the cells for metabolism. In order to overcome insulin resistance, the pancreas will secrete a large amount of insulin, resulting in blood insulin levels much higher than normal, which is the so-called “hyperinsulinemia”. In the early stage of obesity, the human body can barely maintain blood glucose in the normal range by secreting more insulin, then the function of the pancreas to synthesize insulin gradually fails, and insulin production is not enough to maintain blood glucose in the normal range, so overt diabetes occurs. The ability of bariatric surgery to treat type 2 diabetes stems from the discovery that after surgical treatment of obese patients with concomitant diabetes, blood glucose has returned to normal while weight loss is still well underway. After nearly 10 years of research, it has been confirmed that weight loss surgery can effectively control type 2 diabetes. As a result, “bariatric surgery”, which used to focus on weight control, has become “bariatric and metabolic surgery”, which treats metabolic diseases, mainly diabetes, at the same time. Diabetes, an ancient disease, has a new treatment. The largest meta-study of surgical treatment for diabetes published in the United States so far analyzed 16,944 patients and showed that 77% of the patients had complete or partial remission of diabetes after bariatric surgery, i.e., the blood glucose indexes were maintained within the normal range without medication or with reduced medication. In 2012, the New England Journal of Medicine published data showing that weight loss surgery can achieve complete remission in 85% of patients with type 2 diabetes with obesity, and its effect is better than drug treatment. In response, the International Diabetes Federation issued a statement recognizing bariatric surgery as an effective treatment for type 2 diabetes. Which diabetic patients are suitable for surgical treatment? The currently accepted ABCD criteria in China are: A (age) less than 65 years old; B (BMI) body mass index greater than 27.5; C (C peptide, an indicator of pancreatic islet cell function) greater than one-half of the lower limit of normal; and D (duration) diabetes disease less than 15 years. Patients with diabetes who meet this criterion can achieve better results with surgery. The basic methods of diabetes surgery are mainly gastric bypass and gastric sleeve resection. Both involve several small holes in the abdominal wall and a laparoscopic surgical operation. The former involves truncating the stomach and making an anastomosis with the small intestine. The latter is a longitudinal resection of the stomach to reduce its size to a banana-shaped stomach. This surgical procedure is relatively simple. Due to the presence of digestive tract continuity, the effect of surgery on systemic nutrition is relatively mild. In addition to the reduction in food intake and weight loss as a result of bariatric surgery, the changes in the gastrointestinal tract cause a series of complex changes in the endocrine function of the body, thus allowing effective control of diabetes.