Objective To investigate the clinical features of pulmonary infection in patients with hepatitis B virus (HBV)-related acute-on-chronic liver failure (ACLF).Methods A total of 666 hospitalized patients with HBV-ACLF in Department of Liver Disease of Fuzhou Infectious Diseases Hospital were retrospectively analyzed.Data of demographic and clinical parameters (sex,age,presence of liver cirrhosis and diabetes),complications (spontaneous bacterial peritonitis,hepatorenal syndrome,hepatic encephalopathy,and upper gastrointestinal hemorrhage),and baseline biochemical parameters were collected from the medical records database.Univariate and multivariate regression analyses were performed to determine the independent risk factors of pulmonary infection in patients with ACLF.Distributions of the pathogenic bacteria were further analyzed.Student t test was used for the means consistent with normal distribution,while non-parametric statistics were used for the data consistent with abnormal distribution.Mann-Whitney U test was used for the data between two groups.Chi square test and Fisher exact probability method were used for comparing the count data.Results A total of 125 out of 666 patients with ACLF developed pulmonary infection.The incidence of pulmonary infection was 18.76 ％ (125/666)..Most patients were infected with fungi (54.84％).The incidence rate of pulmonary infection in patients with liver failure over 60 years (41.18％) was significantly higher than that in patients under 60 years (16.91％;x2 =19.136,P＜0.01).The incidence of cirrhosis or diabetes in the 125 patients with pulmonary infection was higher than patients with no pulmonary infection.The difference between the two groups was statistically significant (P＜0.01).Levels of albumin,cholesterol,alphafetoprotein,white blood cell count,hemoglobin,plasma thromboplastin antecedent,international normalized ratio (INR),and serum sodium were all significantly different between the two groups (all P＜ 0.05).The incidence of spontaneous bacterial peritonitis,hepatorenal syndrome,and hepatic encephalopathy in patients with pulmonary infection were significantly higher than those without pulmonary infection (P＜0.01).Spontaneous bacterial peritonitis,age,albumin,hemoglobin and serum sodium were important factors in the development of the pulmonary infection.And albumin,hemoglobin and serum sodium were protective factors.Conclusions Pulmonary infection,as one of the common and serious complications,significantly affects the prognosis of liver failure patients.Prediction of pulmonary infection in the early stage is essential.Patients with elder age,spontaneous bacterial peritonitis,low albumin level,low serum sodium level and low hemoglobin level should be timely monitored to prevent the development of pulmonary infection.