Abstract: In order to explore the impact of physical exercise on adolescents' academic performance and its mechanisms, using the data from 2013 to 2015 China Education Panel Survey, the impact of physical exercise on adolescents' academic performance was examined by means of hierarchical linear model, and the influencing mechanisms between the two variables through structural equation model and KHB.It is found there is an inverted U-Shaped relationship between the time students spend on physical exercise and their academic performance, with its highest point when reaching 45.6 minutes of daily exercise.The result of multiple mediating effects analysis shows that physical exercise can improve students' academic performance through four mechanisms:reducing students' negative emotions, enhancing interactions among classmates, promoting positive behaviors and building self-confidence.Conclusions are drawn that these findings support the previous "positive effect theory"; persistent and appropriate daily exercise has the best effect on the students' academic performance rather than the largest or contracted time spent on daily exercise does.The students' psychological health, positive behaviour, classmate interaction and self-confidence become the important mediating machanism.The medating machanism of the other two variables including adolescents' BMI and daily average sleeping time are yet to be calculated and tested.