Objective: To investigate the effects of 24 hour movement behaviors on the self confidence level of junior high school students, providing empirical evidence for optimizing physical activity intervention strategies and enhancing adolescents mental health. Methods: In December 2024, a stratified cluster random sampling method was used to select 350 students from 3 junior high schools in Wuhan City. The ActiGraph wGT3X-BT accelerometer was employed to monitor participants 24 hour movement behaviors, and the Children and Adolescents Self confidence Questionnaire was used to assess their self confidence levels. Compositional isotemporal substitution models were applied to analyze the substitution effects among different movement behaviors and their impact on the self confidence level of junior high school students. Results: Among the 24 hour movement behaviors of junior high school students, the compositional means and proportions of moderate to vigorous physical activity (MVPA), light physical activity (LPA), sedentary behavior (SB), and sleep (SP) were 33.91 min (2.35%), 151.64 min (10.53%), 761.12 min (52.86%), and 493.33 min (34.26%), respectively. There were no statistically significant differences were found across grade, parental education level, or family economic status ( t/F =0.62,1.50,-1.22, all P >0.05). Significant differences in self confidence levels were observed between male and female junior high students ( t=3.36, P <0.05). Regarding 24 hour movement behaviors, MVPA, LPA, SB and SP exhibited statistically significant differences across gender, grade, and parental education ( Z/H =-6.76-6.15, all P < 0.05 ). Results of component linear regression analysis indicated that the proportion of MVPA time positively predicted junior high school students self confidence levels ( β =4.38), while the proportion of SP time negatively predicted self confidence levels ( β = -11.20 ) (both P <0.05). Isotemporal substitution analysis revealed that replacing 15 minutes of SB and SP with MVPA increased total self confidence scores by 1.53 and 1.97 units, respectively, while the opposite substitution decreased scores by 2.48 and 2.91 units (all P <0.05). Dose response analysis revealed an asymmetric pattern in the isochronous substitution effects between MVPA and SB/SP. Conclusions The overall distribution of 24 hour movement behaviors significantly impacts self confidence level of junior high school students. Insufficient MVPA may constrain the positive development of self confidence.