Inclusion Criteria:  reported snore, apnea and daytime sleepiness; a diagnosis of obstructive sleep apnea with polysomnography according to ASSM guideline(apnoea-hypopnea-index(AHI)≥5 events/h) and need to be treated with continuous positive airway pressure; willing to participate after informed consent.  Exclusion Criteria:  Evidence of severe coronary or cerebral, cardiovascular disease and significant memory, perceptual or behavioural disorder; Severe respiratory disease defined as severe chronic obstructive pulmonary disease(ie. FEV1/FVC<70% and FEV1<50%predicted) or resting awake SaO2<90% Have known contraindications with CPAP, like current pneumothorax and hemoptysis, et al. Central sleep apnea>10 events/h； Frequent nasal congestion； Optimal treatment CPAP pressure(by manual titration) equal or higher than 10cmH2O.