ObjectiveTo evaluate the effect of selective decontamination of digestive tract(SDD) on preventing ventilatorassociated pneumonia by Metaanalysis based on theory and method of evidencebased medicine. MethodsSix medical databases ( PubMed， Excerpta Medica Database ［EMBASE］, China Biology Medicine disc［CBMdisc］， China National Knowledge Infrastructure［CNKI］, VIP database, from 1995 to 2014,  and Cochrane Library of issue 12,2014) were searched， literatures were selected, data were extracted, Metaanalysis was performed by using RevMan 5.3 software. Results13 literatures were included (2 676 patients were involved), Metaanalysis revealed that the incidence of VAP in treatment and control group was 20.68% and 35.99% respectively (OR and 95%CI,0.40 ［0.28，0.56］, P<0.001)，the mortality rate of patients with mechanical ventilation in treatment group and control group were 20.60% and 20.03% respectively (OR and 95%CI，0.99 ［0.81，1.20］，P=0.91). ConclusionSDD can  reduce the incidence of VAP in patients with mechanical ventilation, but can’t reduce mortality rate.