Objective: To analyze the correlation between physical activity and physical fitness index of children and adolescents in China, so as to provide reference for physical activity and physical fitness promtion of children and adolescents. Methods: In September 12,2018, 4 269 students were selected by cluster sampling in east, northwest, north, central, southwest and South China, the test of standing long jump, grip strength, 50 m running, improved seat forward bend, 30 s sit ups, 20 s cross repeatedly, 20 m round trip running was completed. Results: In comparing the physical fitness index of children and adolescents with different levels of physical activity, the PFI values of the middle and high intensity physical activity (MVPA) groups of boys aged 10-12 and 16-18 years old were (0.46±3.58) (0.75±3.0), the value of PFI of the MVPA group were (-0.69±3.64) (-0.61±2.87), the difference was statistically significant ( t =0.04, 0.57, P >0.05). There was no significant difference in the values of PFI between the four age groups of the girls ( P <0.05). In comparison of physical activity status of children and adolescents in different physical ability grades, the time of MPA, VPA and physical exercise in healthy physical ability group was higher than that in unhealthy physical ability group ( Z =-2.04, -4.93, -7.09, P <0.05). Linear regression analysis showed that there was a positive correlation between daily MVPA, physical exercise and physical fitness index ( P <0.05). Conclusion Moderate and high intensity physical activity, that is, physical exercise, is positively correlated with physical fitness index. Therefore, it is particularly important for children and adolescents to engage in sufficient moderate and vigorous intensity physical activities.