Objective:To explore the brain electrical activity and its correlation with polysomnography monitoring parameters in children with obstructive sleep apnea syndrome (OSAS) and primary snoring.Methods:It was a prospective observational study involving children aged 6-12 years who presented to the Sleep Center of Beijing Children′s Hospital, Capital Medical University for polysomnography monitoring due to snoring at sleep from July 1 to December 31, 2019.Clinical data, polysomnography monitoring and 6-min measurement of brain electrical activity were collected from all the subjects.According to the results of polysomnography monitoring, the subjects were divided into the primary snoring group and the OSAS group at varying degrees.Based on the electroencephalogram (EEG) wavelet analysis, the brain injury index obtained by EEG synchronization and complexity analysis was used to reflect the changes of brain electrical activity in children in the resting state.Rank sum test was used to test the differences in brain injury index and the percentage of each frequency band of brainwave.Multivariate linear regression method was used to analyze risk factors for EEG activity.Results:A total of 149 children were recruited, including 110 males and 39 females.There was no significant difference in the proportions of α, θ, β and δ waves among OSAS children at varying degrees(all P>0.05). The brain injury index of the primary snoring group, mild OSAS group, moderate OSAS group and severe OSAS group was 0 (0, 3), 14 (9, 16), 26 (24, 28), and 34(30, 44), respectively.There were statistically significant differences in the brain injury index among groups ( H=129.70, P<0.01). The brain injury index gradually increased from the primary snoring group to the severe OSAS group.Multivariate linear regression analysis showed that the obstructive apnea hypopnea index (OAHI), mean oxygen saturation and minimum oxygen saturation were independently correlated with the brain injury index (all P<0.05). Conclusions:There were no significant differences in the ratios of α, θ, β and δ waves among OSAS children at varying degrees, while the EEG complexity and synchronicity varied a lot.With the increase of OAHI, the brain injury index gradually increased.The brain injury index was independently correlated with OAHI, mean oxygen saturation and minimum oxygen saturation.