Objective To explore the differences of sleep structure parameters in patients with obstructive sleep apnea (OSA) at different ages and the relationship with brain functional status. Methods A total of 200 OSA patients admitted to our hospital from April 2019 to May 2022 were selected as the study subjects, and the patients were divided into the young group (<40 years old), the middle-aged group (41-65 years old), and the elderly group (>65 years old) according to age. After 1∶1∶1 matching, 48 patients were in each of the three groups, and their clinical data were compared.Polysomnography (PSG) was used to measure sleep structure parameters and resting state electroencephalography (rs-EEG) to measure daytime brain function. Logistic regression was adopted to analyze the relationship between sleep structure parameters and daytime brain function status. Receiver operating characteristic (ROC) curve was used to analyze the diagnostic value of PSG results and brain function status in different age groups. Results The number of fast wave sleep, N2 sleep ratio, rapid eye movement (REM) sleep ratio, brain chaos index, external concentration index and internal concentration index in the middle-aged group were higher than those in the young and elderly groups. The number of slow wave sleep, endogenous anxiety index and reaction speed index in the middle-aged group were lower than those in the young group, and the differences were statistically significant (P<0.05). The multivariate analysis results showed that the number of slow wave sleep, the number of fast wave sleep, N2 sleep ratio and REM sleep ratio were independent risk factors for changing daily brain function status in OSA patients of different ages. The number of slow wave sleep was negatively correlated with brain chaos index, response speed index and internal concentration index. The number of fast wave sleep and N2 sleep ratio were positively correlated with brain chaos index and external concentration index. The REM sleep ratio was positively proportional to brain chaos index, endogenous anxiety index and internal concentration index. In the middle-age group, when the apnea hypopnea index (AHI) was ≥5, ≥15 and ≥30 times/h, the number of fast wave sleep, N2 sleep ratio and REM sleep ratio were highly predictive for the diagnosis and severity of OSA. The number of fast wave sleep, when AHI≥30 times/h, could highly predict the diagnostic value of moderate and severe OSA in the young group, and the N2 sleep ratio and REM sleep ratio could highly predict the diagnostic value of moderate OSA in the elderly group. Conclusions The sleep and brain status of OSA patients are significantly different in different age stratification. OSA patients aged 41 to 65 have the worst sleep quality and significant changes in daily brain function status. And in those from 41 to 65, their number of slow wave sleep, number of fast wave sleep, N2 sleep ratio and REM ratio have the highest diagnostic value for daytime brain function.