Objective: To analyze the effect of a comprehensive intervention on the accuracy of children s body size perception, so as to provide a theoretical basis for child body size perception improvement. Methods: The participants were selected from a cluster randomized controlled trial (September 2018 to June 2019). A total of 1 287 children in 24 primary schools (clusters) equally distributed among three regions (Beijing, Changzhi and Urumqi) were selected, which included 12 intervention schools (648 students) and 12 control schools (639 students). The accuracy of body size perception was measured by Ma figural stimuli. A linear mixed model was employed to analyze the effect of the comprehensive intervention on the accuracy of children s body size perception. Results: At baseline, the accuracy rate of body size perception among children in the intervention group and the control group was 56.6% and 51.5%, respectively. The underestimation rate was 42.0% and 47.7%, and the overestimation rate was 1.4% and 0.8%. After the intervention, compared with the control group, the inaccuracy rate ( OR=0.50, 95%CI=0.37-0.68, P <0.01) and the underestimation rate in the intervention group decreased ( OR=0.37, 95%CI=0.26-0.54, P <0.01). There was no significant difference in the overestimation rate between the two groups( P =0.51). The results of the stratified analysis showed that the intervention could improve the accuracy of children s body size perception, regardless of their gender, nutritional status, region, or whether or not they were only child( P >0.05). Conclusion The inaccuracy rate of children s body size perception, which mainly involved underestimation was high. A comprehensive intervention can effectively reduce body size underestimation and improve the accuracy of children s body size perception.