Objective: To explore the association between interaction effects of dietary behaviors and caregivers s type on overweight or obesity among left-behind children, and to provide a reference for overweight or obesity prevention among the left-behind children. Methods: From October to December 2018, 877 left-behind children aged 7-18 years were randomly selected from a stratified cluster in county, Shangrao City, Jiangxi Province.Type of caregives, dietary behavior, health status were collected from questionnaires, height, weight were examined. Results: The detection rate of overweight and obesity in left-behind children was 21.7%(190/877), and the rate of overweight and obese left-behind children with other foster parents was 29.8%(158/530), higher than the rate of 16.2%(32/198). The detection rate of overweight and obesity of left-behind children who consumed high level of western fast food was 59.0%(59/100). There were significant differences in rate of overweight and obesity by type of caregiver and western food consumption. Regression analysis showed that the detection rate of overweight and obesity of left-behind children who often ate western fast food was 5.70 times(95%CI=3.62-8.99) high than that of those who seldom ate western fast food. Interaction analysis showed that the interaction(synergistic effect) of the type of adopter × whether the adopter often ate western fast food(father or mother × yes) presents a positive multiplying interaction(synergistic effect). Left-behind children under paternal or maternal care together with high western fast food consumption greatly increased the risk of overweight and obesity(OR=6.94, 95%CI=2.76-17.44). Conclusion Frequent consumption of western fast food together with one parent stay at home is associated with overweight and obesity of left-behind children. These two factors have a synergistic effect, which greatly increases the risk of overweight and obesity of left-behind children. In other words, their interaction is a major risk factor.