Objective: To explore the barriers to physical activity behavior among overweight and obese children and adolescents, so as to provide evidence for developing physical activity intervention programs. Methods: From March to April 2025, 13 overweight or obese children and adolescents from one primary school and one secondary school in Nanjing were selected by purposive sampling for semi structured interviews. Guided by the capability, opportunity and motivation-behavior model, data were coded, categorized and analyzed using content analysis. Results: A total of 13 interviews were completed, with a cumulative duration of 358 minutes. Three themes and eight subthemes were identified:capability factors, including physical discomfort and limited physical fitness, weak exercise skills and insufficient behavioral regulation ability, and insufficient psychological capability; opportunity factors, including insufficient family support and negative influence, pressure from school and peer environments, and limited time resources and exercise conditions; and motivation factors, including low self efficacy and situations prone to giving up, and insufficient positive feedback and lack of attractiveness of exercise forms. Conclusions Barriers to physical activity among overweight and obese children and adolescents result from the combined effects of capability, opportunity and motivation. It is necessary to lower the threshold for initiating exercise, strengthen positive experiences and feedback, and build integrate family-school support environments to promote the initiation and maintenance of physical activity behaviors in children and adolescents.