China has one of the highest rates of cesarean sections in the world. However, limited epidemiological studies have evaluated the risk factors for cesarean section among Chinese women. Thus, the aim of this cohort study was to investigate the associations between pre-pregnancy BMI, gestational weight gain (GWG) and the risk of cesarean section in China. A total of 57,891 women with singleton, live-born, term pregnancies were included in this analysis. We found that women who were overweight or obese before pregnancy had an elevated risk of cesarean section. Women with a total GWG above the Institute of Medicine (IOM) recommendations had an adjusted OR for cesarean section of 1.45 (95% CI, 1.40-1.51) compared with women who had GWG within the IOM recommendations. Women with excessive BMI gain during pregnancy also had an increased risk of cesarean section. When stratified by maternal pre-pregnancy BMI, there was a significant association between excessive GWG and increased odds of cesarean section across all pre-pregnancy BMI categories. These results suggest that weight control efforts before and during pregnancy may help to reduce the rate of cesarean sections.