Objective To review the changes of gut microbiota after bariatric surgery and the related mechanisms of improving metabolism. Method Domestic and international literatures in recent ten years on the changes of gut microbiota in bariatric surgery and the mechanisms of improving metabolism were collated and summarized. Result The common bariatric procedures performed to date were vertical sleeve gastrectomy (VSG) and laparoscopic Roux-en-Y gastric bypass (RYGB). The changes of gut microbiota vary in different surgical procedures, which were related to the changes of diet habits, gastrointestinal anatomy, gastrointestinal hormone levels and metabolic complications. The gut microbiota might improve the body metabolism by regulating the levels of short chain fatty acids, branched chain amino acids and bacterial endotoxin in the intestinal lumen. Conclusions Significant changes are found in gut microbiota after bariatric surgery, which may be involved in the improvement of body metabolism by regulating the level of bacterial endotoxin and microbial metabolite. However, more in-depth mechanisms need to be further clarified.