Objective To assess the effectiveness of the auto-continuous positive airway pressure (Auto-CPAP) versus the fixed-continuous positive airway pressure (Fixed-CPAP) in patients with obstructive sleep Apnea syndrome (OSAS). Methods Such databases as PubMed (1990 to 2010), SpringerLink (1995 to 2010), CNKI (1990 to 2010), WanFang Data (1995 to 2010), and Google academic (1994 to 2010) were searched, the relevant conference theses were retrieved, and the experts in this field were enquired to collect the randomized controlled trials (RCTs) on Auto-CPAP versus Fixed-CPAP for patients with OSAS. Two reviewers independently screened the trials according to inclusion and exclusion criteria, abstracted the data, and assessed the methodology quality. Meta-analyes was performed using RevMan 5.0 software. Results A total of 11 RCTs involving 327 patients were included. The results of meta-analyses showed that, compared with the Fixed-CPAP group after treatment, the Auto-CPAP group significantly reduced the mean effective therapeutic pressure (WMD=-1.79, 95%CI -3.39 to -0.20), won much better treatment adherence (WMD=0.43, 95%CI 0.30 to 0.56), but got much higher scores of the Apnea-hypopnea index (AHI) (WMD=1.17, 95%CI 0.25 to 2.08) and Epworth Sleepiness Scale (ESS) (WMD=0.88, 95%CI 0.42 to 1.33) as well. There was no significant difference between those two groups in patients’ subjective preference for treatment (OR=2.06, 95%CI 0.46 to 9.10). Conclusion Compared to the Fixed-CPAP, the Auto-CPAP significantly reduces the mean effective therapeutic pressure and improves the treatment adherence of the patients, but is inferior in decreasing AHI and ESS. However, more high-quality and large-scale RCTs are required to verify the above conclusion because of the limitation of research quality and sample at present.