Objective: To examine the effects of high intensity interval training (HIIT) on body composition and cardiorespiratory fitness of obese primary school students, so as to provide a theoretical basis and practical reference for HIIT exercise prescription in schools. Methods: From August to December 2022, 25 obese children [age:(11.0±0.4)years, BMI:(23.3±0.8)kg/m 2] from a primary school in Shenzhen were recruited and divided into an exercise group ( n =13) and a control group ( n =12). After 12 weeks of exercise intervention [The durations of load period and intermittent period were 15 s, load exercise intensity was 100% maximal aerobic speed (MAS), and intermittent exercise intensity was 50% MAS, each time there were 2 groups× 8 rounds, and the rest between groups was 2 minutes, totaling 10 minutes, and 20 meter shuttle run test (20 m-SRT) was performed once every 4 weeks to adjust and update MAS], the changes in body composition and cardio respiratory fitness indexes of obese subjects before and after the intervention were compared. Results: After the intervention, body weight, BMI, body fat, body fat percentage, and visceral adipose tissue area of obese subjects in the exercise group decreased from (55.6±6.2)kg, (22.7±0.6)kg/m 2, (41.8±6.9)kg, ( 23.4± 5.5)% and (102.4±39.0)cm 2 to (52.3±5.8)kg, (21.1±0.8)kg/m 2, (38.6±6.3)kg, (20.2±4.5)% and (84.2±26.9)cm 2, respectively( t =8.73, 10.96, 7.02, 4.92, 4.95, P <0.05). SBP decreased from (115.4±9.7)mmHg to (112.3±8.7)mmHg ( t = 2.96 , P <0.05). The content of skeletal muscle, 20 m-SRT and VO 2max increased from (21.3±5.3)kg, (21.6±4.9) times and (39.4±2.0)mL/(kg ·min) to (21.8±5.2)kg, (31.4±6.3)times and (43.6±2.6)mL/(kg ·min), respectively ( t =-3.33, -8.37, -10.56 , P <0.05). Conclusions HIIT is an effective way to improve the body composition and cardiorespiratory fitness of obese primary school students. It is recommended that schools with the necessary conditions use this method as an intervention measure to help reduce weight and improve cardiovascular health among obese students.