Surgery has been accepted as a new approach for the treatment of type 2 diabetes mellitus (T2DM). At present, gastric bypass is the high-profile operation method and gradually applied clinically. It showed significant effect in the treatment of T2DM, especially for the T2DM patients accompanied with obesity and even achieve the purpose to control blood glucose and its complications. However, the underlying mechanism of gastric bypass in treating T2DM is quite complex, including the changes in gastrointestinal hormones, the action of fat factor, bile acid metabolism, etc.