Objective: To understand the association between weight-adjusted-waist index (WWI) and cardiopulmonary endurance among middle school students, so as to provide references for the improvement of cardiopulmonary endurance levels in adolescents. Methods: From June 2015 to December 2018 by using the method of purposive sampling, height, weight, waist circumference, and 20 m shuttle-run tests were measured among 44 870 adolescents aged 13-18 from Northeast, North, East, South, Southwest and Northwest of China. The WWI of the adolescents and the maximum oxygen uptake (VO 2max ) were calculated indirectly. The t-test and one way analysis of variance were used for comparison, and the curve regression analysis method was adopted to analyze the relationship between WWI and VO 2max . Results: For Chinese middle school students aged 13-18, the WWI was (9.35±1.02), the number of 20 m shuttle-run was (38.89±18.14) times, and VO 2max was (39.96±5.88) mL/(kg ·min -1 ). The differences of VO 2max between WWI quartile arrays of boys aged 13-18 were statistically significant ( F=15.19, 9.00, 14.97, 20.48, 28.13, 10.13 , P <0.01), girls had the same trend ( F=23.36, 16.61, 33.45, 32.96, 18.23, 19.36, P <0.01). There was an inverted U shaped curve relationship between WWI and cardiopulmonary endurance. When WWI was 8.5, the VO 2max level reached the highest, which was 40.07 mL/(kg ·min -1 ). Compared with girls, WWI in boys had a more significant impact on cardiopulmonary endurance. Conclusion Maintaining optimal WWI levels may enhance adolescents cardiopulmonary endurance.