Abstract: Objective To analyze the association between school-level policy on physical activity (PA) and Body Mass Index (BMI) among primary school students,providing scientific evidences for obesity prevention and intervention.Methods A sum of 1 889 students of grade 3-5 frorm 12 primary schools in one district of Beijing were recruited through cluster sampling,body weight and height were measured.Dietary pattern and moderate to vigorous physical activity (MVPA) were accessed by self-report questionnaire.School doctors or PE teachers reported PA associated policy in school.Multi-level model was used to analyze the association between school-level policy and BMI Z-score of students.Results The BMI Z-score of boys and girls was (0.61±1.21)and (-0.04±1.13),separately(P<0.01).Dietary scores were (3.39±0.80) and (3.38±0.77) in of boys and girls,respectively(P=0.874).About 20.28% of boys reported 1 hr/d MVPA,significantly higher than that of girls(11.92%) (P<0.01).The median score of school PA policy was 5,ranging from 3 to l0.After adjusting age,gender,dietary score and MVPA in the multi-level model,BMI Z-score was decreased by 0.15 (P=0.017) in students in school PA policy ≥5 than students from school PA policy score <5.Conclusion School-level physical activity policyis closely related to weight statues of students,further supporting childhood obesity prevention strategies which focusing on school-based physical activity policy initiatives.