Abstract: Objective Pseudomonas aeruginosa is the main strain of nosocomial infection with a high drug resistance.The aim of this paper is to investigate the epidemiology and risk factors of Pseudomonas aeruginosa infection in patients with severe thoracic trauma and mechanical ventilation,so as to provide basis for clinical prevention and treatment of ventilator-associated Pseudomonas aeruginosa. Methods Total 218 patients with severe chest trauma and mechanical ventilation in our hospital from January,2012 to January,2016 were prospectively collected.The primary outcomes included the epidemiology and risk factors of Pseudomonas aeruginosa infection,and the secondly outcomes included drug resistance of Pseudomonas aeruginosa. Results A total of 21 cases (9.63%) developed Pseudomonas aeruginosa infection.The diagnosis was confirmed at 3 to 47 days after mechanical ventilation,and the average infection days was (19.57±6.38) days after mechanical ventilation.When compared with the control group,patients in the study group got a significantly longer duration of mechanical ventilation,a higher rate of open injury,a higher level of APACHEⅡ score,a higher rate of more than 3 kinds of antibiotics usage,a higher rate of thoracotomy,a higher rate of hematopneumothorax and a higher rate of multiple injuries (P<0.05).Single factor and multi factor regression analysis showed that the duration of mechanical ventilation,APACHE score and thoracic surgery were risk factors of Pseudomonas aeruginosa infection in severe thoracic trauma patients with mechanical ventilation (P<0.05).In the 21 strains of Pseudomonas aeruginosa,18 strains were multi-drug resistant bacteria,2 strains were extensively drug resistant bacteria.The drug resistance rate of Pseudomonas aeruginosa resistant to imipenem and meropenem were lower (14.29%). Conclusion The Pseudomonas aeruginosa infection rate and drug resistance rate in patients with severe thoracic trauma and mechanical ventilation are high,and duration of mechanical ventilation,APACHE score and thoracic surgery were risk factors of Pseudomonas aeruginosa infection in severe thoracic trauma patients with mechanical ventilation.The prevention and treatment of this type of Pseudomonas aeruginosa may improve patients'outcomes.