Objective: To evaluate the effect of a dietary and exercise intervention on cognition and behaviors among primary school students, and to further explore the mediating role of family support, in order to provide scientific evidence for future effective intervention strategies. Methods: A dietary and exercise intervention program for childhood obesity prevention was carried out in 24 primary schools in Beijing, Changzhi and Urumqi from 2018 to 2019, and 1 392 children in grade four as well as their parents were included. Family support and children s cognition and behaviors were collected through questionnaire. To carry out diet and exercise behavior intervention on the three levels of school, family and individual in the intervention group,and children s dietary and exercise knowledge, eating habits, physical activities, as well as sedentary and screen behaviors were evaluated. The linear mixed model was used to analyze the effect of intervention on children s cognition and behaviors, and the mediation model was used to explore the role of family support. Results: The proportion of children with higher score of dietary and exercise knowledge ( OR= 2.34 , 95%CI =1.71-3.21), eating habits ( OR=2.58, 95%CI =1.75-3.82), and sedentary and screen behaviors ( OR=1.91, 95%CI =1.35-2.68) increased in the intervention group after one year intervention ( P <0.01), compared with the control group, respectively. The intervention also increased the proportion of children s family support in the intervention group compared with the control group ( OR=3.45, 95%CI =2.19-5.45), and the support from children s fathers ( OR=2.70, 95%CI =1.68-4.35), mothers ( OR=3.71, 95%CI =2.28-6.04), paternal grandmothers ( OR=1.65, 95%CI =1.00-2.70), and maternal grandmothers ( OR= 2.14, 95%CI =2.12-2.16) increased significantly ( P <0.05). The mediation analysis showed that family support played a mediating role in association between comprehensive intervention and children s eating habits as well as sedentary and screen behaviors. Conclusion The dietary and exercise intervention effectively promoted children s cognition and behaviors, and family support played an important mediating role.