Objective: To explore the intervention effect of different intensity of classroom physical exercise on cardiorespiratory fitness and executive function of Tibetan first grade students at high altitude, so as to provide reference for improving the level of cardiorespiratory fitness and executive function of Tibetan adolescents. Methods: From September to December 2020, 184 Tibetan students from five first grade classes in a middle school in Lhasa, Tibet, were randomly assigned into a control group (81 students in two classes) and an intervention group (103 students in three classes). Both groups followed the same teaching programme, but the intervention group received 36 sessions of moderate to high intensity classroom physical activity, one session per day, Monday,Wednesday and Friday, for 12 weeks. Before and after the intervention, cardiorespiratory fitness and executive function were tested by 20m round trip running and Flanker s experimental paradigm, 2-back s experimental paradigm, and More odd shifting experimental paradigm for inhibitory control, refreshing memory, and switching flexibility, and the results were analysed by analysis of covariance (ANCOVA) to compare the results of the pre and post intervention periods. Results: The maximum oxygen uptake (VO 2max ) of Tibetan first grade students in the intervention group increased by 2.25 mL/(kg〖WW）〗·〖WW(〗min) compared with the control group after the intervention ( t =-3.89, P <0.01); the response time of the inhibitory function was reduced by 4.40 ms, that of the refreshing function by 196.06 ms, and that of the switching function by 92.72 ms in the intervention group compared with the control group ( t =2.98, 4.82 ,3.21, P <0.05). Conclusion The 12 week moderate to high intensity classroom physical activity intervention has different degrees of improvement effects on cardiorespiratory fitness and executive function in Tibetan adolescents.