Objective To compare the effectiveness between continuous aspiration of subglottic secretion(CASS) and intermittent aspiration of subglottic secretion (IASS) in mechanical ventilation patients for preventing ventilator- associated pneumonia (VAP). Methods Randomized controlled trials published from July 1994 to July 2019 were identified by searching CochraneLibrary,PubMed,MEDLINE,EMBASE,Web of Science,China Biology Medicine database, CNKI, Wangfa and VIP Database. Two reviewers independently screened the studies according to the inelusive and exclusive criteria,assessed the quality and extracted the data. Then RevMan 5.3 software was used for Meta-analysis. Results Eighteen studies enrolling a total of 1951 patients met the inclusion criteria. Meta-analysis showed no significant difference between two groups for the incidence of VAP,time to VAP occurrence,the aspirated secretion volume,duration of mechanical ventilafion,length of ICU stay (P>0.05). The positive rate of occult blood test in CASS group was higher (P<0.01).Conclusion The results indicate no significant differences between the two groups for preventing VAP. But the risk of tracheal wall injury in CASS is higher than that in IASS.