Objective: To analyze the association of 24 h activity behaviors and physical health of primary school students, so as to provide a reference for promoting the physical health of children and adolescents. Methods: From May to June, 2023, by stratified random sampling method, 583 primary school students aged 7-12 were selected from Tianjin for physical health examination. ActiGraph GT3X+ was used to measure their 24 h activity behaviors for 7 d, and their mental health and 24 h activity behaviors were analyzed by gender and grade. LASSO regression was applied for assessing the impact of 24 h activity on their health. Results: The compliance rate of seated forward bending (93.12%) were higher in boys than girls (91.86%), and the differences were statistically significant ( χ 2=4.53, P <0.05). Sleep time ( β =0.06), light intensity physical activity (LPA) time ( β =0.11), and moderate to vigorous physical activity (MVPA) time ( β =0.14) were positively correlated with physical fitness, whereas sedentary behavior (SB) time ( β =-0.08) were negatively correlated with physical fitness, and MVPA time had a positive effect on physical health of children and adolescents, followed by LPA time; while sleep time also had a positive effect , and SB time had a negative effect ( P <0.05). Conclusions Primary school students are generally faced with low physical activity level and high SB time, and MVPA and LPA have a significant impact on physical health. Therefore, it is crucial to develop personalized and differentiated physical activity promotion policies and interventions for primary school students with different classmates and gender.