Objective：To investigate the effect of bedside angle instrument on preventing ventilator associated pneumonia（VAP） of patients underwent mechanical ventilation（MV）． Methods：Totally 81 patients underwent MV were divided into experimental group（n=42） and control group（n=39）. The head of bed in control group was elevated according to nurse’s experiences while head of bed in experiment group was elevated by bedside angle instrument. Bed elevation angle and positive rate of same bacterial culture in gastric juice，throat swab specimens and bronchial secretion liquid between two groups were measured and analyzed. Results：Accuracy of bed head elevation in experimental group（100.00%） was higher than that of control group（57.69%），with statistical differences. Posi－tive rate of related body fluid bacteria was 26.19% in experiment group and 64.10% in control group，with statistical differences. Inci－dence of VAP was 21.42% in experiment group and 48.71% in control group. Conclusions：Bedside angle instrument can ensure the accuracy of bed head elevation，contribute to posture nursing and finally decrease the rate of VAP.