Objective To review recent advancement of the relationship between obesity and gastric cancer. Method We searched PubMed, Medline, EMBASE, Cochrane Library databases, CNKI, and WanFang database for recent clinical trials about the impact of obesity on occurrence, surgery outcomes, and prognosis of gastric cancer. Results Obesity significantly increased the risk of adenocarcinoma of esophagogastric junction (AEG), increased difficulty in radical operation of gastric cancer and complications of perioperative period, but it had no effect on the long-term operative outcomes. The association between obesity and the survival of gastric cancer was not clear. However, the better survival was observed in most researches of gastric cancer patients with excess body weight. Conclusions The relationship between obesity and gastric cancer is very complex, and there is no consistent conclusion. A reasonable body weight by a healthy lifestyle is expected to decline the incidence of AEG.