Objective To explore the relationship between high birth weight and childhood obesity, so as to provide scientific evidence for preventing and reducing childhood obesity. Methods A total of 70 284 Shanghai children aged 3-12 years were selected by multi-stage stratified cluster random sampling method. The age, gender, body weight, height, neonatal period data (including gestational week, birth weight and feeding pattern) were collected by questionnaire, and the relationship between high birth weight and childhood obesity was analyzed. Results There were significant differences in proportions of overweight, obesity and severe obesity between the high and normal birth weight groups (all P<0.05) in both boys and girls. After adjusting for age and gender by multivariate logistic regression model, we found that high birth weight was an independent risk factor for childhood overweight (OR=1.41, 95% CI 1.33-1.51, P<0.05), obesity (OR=1.45, 95% CI 1.31-1.62, P<0.05) and severe obesity (OR=1.51, 95% CI 1.35-1.68, P<0.05). After adjusting for age, gender and neonatal characteristics (including gestational week and feeding pattern), we found that high birth weight was still an independent risk factor for childhood overweight (OR=1.40, 95% CI 1.31-1.50, P<0.05), obesity (OR=1.44, 95% CI 1.28-1.61, P<0.05) and severe obesity (OR=1.42, 95% CI 1.25-1.60, P<0.05). Conclusion High birth weight is an important risk factor for overweight, obesity and severe obesity in children.