Objective To investigate the related factors of nosocomial infection after severe thoracic trauma so as to provide basis and interventions for lowering nosocomial infection rate.Methods A retrospective case series study was conducted in 148 cases of severe thoracic trauma surgically treated from January 2014 to January 2016.There were 98 males and 50 females with an average age of 34.7 years.The abbreviated injury scale (AIS) was ≥ 3 points.The incidence of nosocomial infection was statistically analyzed.The possible factors related to nosocomial infection were analyzed,including age,gender,previous basic diseases,coma,blood transplantation,surgical procedure,operation time,tracheal intubation time,postoperative tracheotomy,and postoperative ICU hospitalization.Results Nosocomial infection occurred in 18 cases,with infection rate of 12.2％.There were 11 cases of pulmonary infection,four urinary tract infection,two incision infection,and one thoracic cavity infection.There were four cases (22％) of Gram-positive bacteria as pathogen,both of which were Staphylococcus aureus.A total of 12 cases (67％) were Gram-negative bacteria,among which four were infected with Klebsiella pneumonia,three with Acinetobacter baumannii,three with Pseudomonas aeruginosa,and two with Escherichia coli.Two cases were infected by fungi.The incidence of infection was correlated with the patients' age (≥ 60 years),previous basic disease,coma,operation methods,operation time (≥3 hours),endotracheal intubation time (≥24 hours),tracheotomy after surgery,and postoperative hospitalization duration in the ICU (P ＜ 0.05),rather than gender and blood transplantation.Conclusions The most common pathogen of nosocomial infection in severe thoracic trauma patients is Gram-negative bacteria.The older age,previous basic diseases,coma,thoracotomy,long operation time,long tracheal intubation time,tracheotomy and long ICU hospital stay are the risk factors for nosocomial infection.More attention should be paid to these risk factors in order to minimize the occurrence of postoperative hospital infection,and to reduce the harm to patients.