Objective To analyze the characteristics and influencing factors of sleep disorders and nocturnal hypoxemia of patients with different degrees of obstructive sleep apnea-hypopnea syndrome (OSAHS). Methods Four hundred and twenty-five patients with snoring were scored by Epworth Sleepiness Scale ( ESS), and monitored by polysomnography (PSG). The possible correlations between sleep structure, hypoxia parameters, ESS and clinical features were analyzed and compared in those patients. Results Four hundred and twenty-five patients were divided into 4 groups according to the apnea-hypopnea index (AHI). There were 65 primary snoring patients (15.3%) and 360 OSAHS patients (84. 7% ) including 187 patients (44. 0% ) in severe OSAHS group. ESS was increased as aggravation of OSAHS. There were significant statistical differences in ESS among each group. Compared with primary snoring group, sleep efficiency, NREM1 + 2, oxygen desaturation index ( ODI), time with pulse oxygen saturation below 90% (T(SpO2 <90% ) ) were significantly higher in the OSAHS groups, and NREM3 +4, lowest pulse oxygen saturation level ( LSpO2 ) were lower. ESS was correlated positively with AHI (r= 0. 474,P <0. 01 ). They were both correlated positively with ODI, T (SpO2 <90% ) and NREM1 + 2( ESSr =0. 392, 0. 356,0. 194;AHI r = 0. 714, O. 682, 0. 365, all P < 0. 01 ), and correlated negatively with LSpO2, NREM3 + 4 ( ESS r = - 0. 414, - 0. 196; AHI r = - 0. 740, - 0. 385, both P < 0. 01 ). LSpO2, ODI and T (SpO2 < 90% ) were the primary influencing factors. Common clinical presentations and subjective symptoms were presented including daytime sleepiness, impaired memory, fatigue, dry mouth, oppressive wake and morning headache, etc. Percentage of individuals with daytime sleepiness in the severe OSAHS group was 73. 3% (137/187). These had serious impact on the patients' quality of life, leading to difficulty concentrating, poor memory and cognitive impairment. Conclusions Sleep disorders are found in the patients with different degrees of OSAHS. The excessive daytime sleepiness interrelated partly with the structure of sleep, and totally with hypoxia parameters. The more severity the patients have, the more nocturnal hypoxia, sleep disorders and higher ESS are found.