ObjectiveTo understand the status of Roux-en-Y gastric bypass (RYGB) surgery for treating type 2 diabetes mellitus, and to summarize its effectiveness and existing problems. MethodThe related literatures which discussed the treatment for type 2 diabetes mellitus by RYGB were reviewed and analyzed. ResultsThe therapeutic effect of RYGB for type 2 diabetes mellitus with obesity was tentatively confirmed.But the underlying mechanism was unclear.And there was no standard length of exclusion of the Roux loop and biliopancreatic loop.Postoperative long-term effect was unknown.Whether RYGB was suitable for non-obese type 2 diabetes mellitus that needed further to be rese-arched. ConclusionsThe mechanism of RYGB surgery in treatment for type 2 diabetes mellitus is complex.With the progress of basic and clinical research, the improvement of surgical technique, the elucidation of the mechanism, the affirmation of the long-term effect, and there are more benefits in patients with type 2 diabetes mellitus.