Objective: To evaluate the effectiveness of a comprehensive intervention for childhood obesity on self-efficacy, weight perception, and stage of behavior change, and to provide a scientific evidence for childhood obesity interventions. Methods: The study was a cluster randomized controlled trial. Twelve primary schools and 1 889 children (aged 7-11 years) from Dongcheng District in Beijing were recruited in September, 2013, and were administered a comprehensive intervention for childhood obesity. Six schools (930) were randomly allocated to the intervention group, and six schools (959) were randomly allocated to the control group. A face-to-face questionnaire survey was carried out, R 4.0.3 software was used to analyze the data, and multiple linear regression model was used to analyze the intervention effect. Results: After the intervention, mean (standard deviation) scores of self-efficacy among children in the intervention and control groups were (4.4±0.9) and (4.2±1.1), respectively. After the intervention, the proportion of children in the intervention group who underestimated or overestimated their body weight was 28.4% and 11.3 %, respectively, while the figures in the control were 37.1% and 6.9%; compared with the control, the risk of underestimating body weight decreased among children in the intervention group( OR=0.64, 95%CI=0.52-0.80, P <0.01), while the risk of weight overestimation increased( OR=1.79, 95%CI=1.26-2.54, P <0.01). After the intervention, the proportion of children in the contemplation or action stage of behaviour change was 65.3% and 83.6%, while the figures in the control group were 59.8% and 69.8 %, respectively; in comparison with the control group, more children in the intervention group were in comtemplation ( OR= 1.28 , 95%CI=1.03-1.59, P =0.02) or action stage of behaviour change( OR=2.59, 95%CI=2.04-3.27, P <0.01). Conclusion The comprehensive intervention for childhood obesity improved self-efficacy, weight perception, and facilitated behavior change, but may increase the risk of weight overestimation.