Objective To evaluate the autonomic nervous function in overweight and obese children. Methods Heart rate variability (HRV) and heart rate deceleration force (DC) of holter electrocardiogram results were studied. Exercise equivalent, exercise time to peak heart rate (HR_max), heart rate recovery at 1 min after exercise (HRR₁), recovery time to resting heart rate, systolic blood pressure at resting period, systolic blood pressure at peak exercise and systolic blood pressure at 3 min during exercise recovery period were used to evaluate autonomic nervous function in overweight and obese children. Results There were 31 children (23 boys and 8 girls) in the obesity group, with an average age of (10.4±2.6) years. There were 69 children (35 boys and 34 girls) in the overweight group, with an average age of (10.9±2.7) years. The control group consisted of 100 children (57 boys and 43 girls) with an average age of (10.2±2.7) years. There were statistically significant differences among overweight, obesity and control groups in standard deviation of normal R-R intervals (SDNN), squares of differences between adjacent NN intervals (RMSSD), averages of NN intervals in all 5-min segments (SDANN), percent of NN 50 in the total number NN intervals (pNN₅₀), low frequency (LF)/high frequency (HF) and DC value (P<0.05). The HR_max, exercise equivalent, HRR₁/HRR_max, the time to recover to resting heart rate, the systolic blood pressure at resting period, the peak exercise systolic blood pressure and the systolic blood pressure/peak systolic blood pressure in the third minute of recovery among overweight, obesity and control groups were statistically significant (P<0.05). Conclusions Overweight and obese children have cardiac autonomic nervous dysfunction, especially impaired vagus nerve function, which requires sufficient attention and active intervention to prevent the occurrence of cardiovascular events.