Objective: To explore the relationship between isochronous substitution and BMI, waist circumference (WC), and body fat rate (FAT) among physical activity (PA), sedentary (SB), and sleep (SLP), so as to provide effective measures for obesity control in adolescents. Methods: A total of 193 adolescents aged 12-15 (90 males and 103 females) was randomly selected, and their height, weight, and BMI were measured using routine testing methods from May to August 2022. The PA, SB and SLP of the participants were measured using a 3D accelerometer (ActiGraph GT3X+). Results: The arithmetic mean value overestimated SLP (40.8%) and SB (39.6%) to some extent, and underestimated LPA (16.1%) and MVPA (3.5%) to some extent. Based on the ISM at 15 min, MVPA was substituted for other activity, BMI Z decreased by 0.17-0.22 units, WC Z decreased by 0.16-0.20 units, and FAT Z decreased by 0.17-0.22 units. The substitution between MVPA and for other activity exhibited significant asymmetry. The effects of MVPA substitutions for SB was the largest, followed by the effects of MVPA substitutions for SLP, and the effects of MVPA substitutions for LPA was the lowest. As MVPA substitutions for other behaviors, it reached its maximum (0.06-0.08 units ) when the MVPA time increased by 5 minutes. Conclusions MVPA plays an irreplaceable role in the control of adolescent obesity . While reducing SB time, MVPA duration should be increased to ensure that the daily MVPA duration is not less than 55 minutes in order to effectively control obesity.