Objective To explore the correlation between overweight, obesity and incidence of type 2 diabetes mellitus (T2DM). Methods Databases including PubMed, EMbase, The Cochrane Library (Issue 3, 2012), CNKI, VIP, CBM and WanFang Data were searched from inception to May, 2012 to collect the cohort studies on the correlation between overweight, obesity and incidence of T2DM. The studies were screened according to the inclusion and exclusion criteria by two researchers independently, the quality was evaluated, the data were extracted, and then meta-analysis was performed using RevMan 5.1 and Stata 11.0 software. Results A total of 8 studies involving 101 864 participants were included. The results of meta-analysis showed that, compared with the normal weight population, the onset risk of T2DM was obviously higher in the overweight (RR=2.59, 95%CI 2.11 to 3.19, Plt;0.000 01), and obese (RR=6.28, 95%CI 4.99 to 7.91, Plt;0.000 01) populations. In the subgroup analysis, the onset risk of T2DM was higher in the western obese population (RR=6.91, 95%CI 5.59 to 8.56) than the eastern obese population (RR=4.19, 95%CI 2.93 to 5.99). Based on the Grading of Recommendations Assessment, Development and Evaluation (GRADE), the quality of the included studies on T2DM developed by overweight and obesity was low and medium respectively. Conclusion Overweight and obesity can increase the onset risk of T2DM which is higher in the female and western obese populations than the male and eastern obese populations respectively.