Objective: To investigate the clustering of health-risk behaviors and its influencing factors among children and adolescents in Yancheng City, Jiangsu Province, so as to provide insights into the prevention and control of health-risk behaviors among children and adolescents. Methods: Students were randomly sampled from 4 primary schools, 4 junior high schools and 4 senior high schools in Yancheng City using a multi-stage stratified cluster random sampling method from September to December 2021. Students' demographics and 12 health-risk factors including unhealthy diet, insufficient physical activity and attempted smoking were collected using the Student's Health Status and Influencing Factors Questionnaire by Jiangsu Provincial Center for Disease Control and Prevention, and factors affecting the clustering of health-risk behaviors were identified using a multivariable linear regression model. Results: A total of 2 925 valid questionnaires were recovered, and the respondents included 1 611 boys (55.08%) and 1 314 girls (44.92%). A total of 2 896 respondents were detected with health-risk behaviors, with a detection rate of 99.09%, and 2 772 respondents were detected with clustering of health-risk behaviors (93.06%). Insufficient sleep, insufficient physical activity and insufficient duration of outdoor activity were predominant patterns of clustering. The median number of health-risk behaviors was 4.00 (interquartile range, 2.00) per capita. Multivariable linear regression analysis showed that boys (β=0.232), grade (junior high school, β=0.519; senior high school, β=0.427), urban area (β=0.241), living at school (β=0.395), family structure (single parental family, β=0.188; other families, β=0.344) and father's education level of primary school and below (β=0.369) were factors affecting clustering of health-risk behavior among primary and high school students. Conclusions The detection of health-risk behaviors is high among children and adolescents in Yancheng City, and insufficient sleep, insufficient physical activity and insufficient duration of outdoor activity are predominant health-risk behaviors. Boys, junior high school and above, urban areas, living at schools, single parents, and fathers with a low educational level lead to a high degree of clustering of health-risk behaviors.