Objective To observe influence of auxiliary treatment of bronchoscopy alveolar lavage on respiratory mechanics index and infection control effect in patients with severe ventilator associated pneumonia (VAP). Methods 84 cases of severe VAP patients were randomly divided into the observation group(n=42 cases)and control group(n=42 cases), control group was given antibiotics and conventional sputum suction lavage treatment, the observation group was given bronchoscopy alveolar lavage and antibiotics. Clinical pulmonary infection score(CPIS)and serum calcitonin level(PTC)were recorded in the two groups before and after treatment. Respiratory mechanics indexes such as the dynamic compliance(Cdyn), the airway peak pressure (PIP), work of breathing(WOB)and airway resistance(Raw)were measured in the two groups before and after bronchoscopy alveolar lavage, and the clinical efficacy of two groups were compared. Results CPIS of the observation group(6.37±1.31),(5.42±1.13),(3.52±0.53)was significantly lower than that of the control group(7.72±1.56),(7.14±1.33),(5.13±0.94)(t=4.295,6.387,5.821,all P<0.05)after 3,5,7 d treatment.PTC of the observation group((4.71±0.85)μg/L,(2.65±0.61)μg/L, (0.62±0.23)μg/L)were significantly lower than those of the control group(5.10±0.92)μg/L,(3.96±0.72)μg/L,(1.31±0.43)μg/L(t=4.295,6.387,5.821,all P<0.05)after 3,5,7 d treatment. Cdyn of the observation group after 1 and 4 h bronchoscopy alveolar lavage(35.39±6.39),(35.59± 5.83)were high those of the control group(26.82±4.63),(25.64±4.28)(t=7.038,-10.462,all P<0.05); WOB(10.08±0.45),(8.10±0.38),PIP(21.28±2.76),(15.29±1.67)and Raw(10.08±0.45),(8.10±0.38) in the observation group after 1and 4h bronchoscopy alveolar lavage were lower those in the control group WOB(0.63±0.17),(0.49±0.12),Raw(13.49±0.50),(11.42±0.42),PIP(27.38±3.10),(23.44±2.60)(1h: t=9.681,3.937,32.853,all P<0.05;4h:t=12.231,6.064,6.313,all P<0.05). Total effective rate of the observation group was obviously higher than that of the control group after treatment(93.3%vs.77.8%,chisquare=5.486,P<0.05). Conclusion Auxiliary treatment of bronchoscopy alveolar lavage has clinical curative effect in patients with severe VAP, the method can effectively decreased PTC level of VAP patients, to acquire lung infection control, and improve the respiratory mechanics parameters. Key words: Pneumonia, Ventilator dependence; Bronchoscopy Alveoler lavage; Respiratory mechanics