Objective To investigate the influencing factors for spontaneous bacterial peritonitis (SBP) in patients with acute-on-chronic liver failure (ACLF),and to provide a reference for clinical diagnosis and prognosis evaluation.Methods A retrospective analysis was performed for the clinical data of 667 patients with ACLF who were hospitalized and treated in our hospital from January 2009 to December 2014,and according to the presence or absence of SBP,they were divided into ACLF group(n =232) and ACLF-SBP group(n =435).The general information,laboratory markers,and incidence of complications were compared between the two groups.The t-test was used for comparison of normally distributed continuous data between groups,and the Mann-Whitney U test was used for non-normally distributed continuous data between groups;the chi-square test was used for comparison of categorical data between groups,and a logistic regression analysis was used to identify independent risk factors for ACLF complicated by SBP.Results The comparison of laboratory markers and comorbidities showed that there were significant differences between the two groups in albumin (Alb) (t =-4.110,P ＜ 0.001),alanine aminotransferase (U =-6.653,P ＜ 0.001),aspartate aminotransferase (t =-8.045,P ＜ 0.001),blood sodium (t =-2.879,P =0.006),prothrombin time activity (t =-2.140,P =0.037),international normalized ratio (t =1.453,P =0.042),hemoglobin (t =-3.446,P =0.001),upper gastrointestinal bleeding (x2 =48.252,P =0.002),hepatorenal syndrome (x2 =16.244,P =0.031),and pulmonary infection (x2 =13.564,P ＜ 0.001).The multivariate logistic regression analysis showed that there were significant differences in Alb (OR =1.119,95 ％ CI:1.052 ～ 1.189),platelet count (PLT) (OR =1.035,95 ％ CI:0.755 ～ 1.084),upper gastrointestinal bleeding (OR =1.117,95 ％ C1:0.072 ～ 1.135),and pulmonary infection (OR =2.275,95 ％ CI:0.978 ～ 5.292) (P =0.002,0.038,0.022,and 0.036).Conclusion In the treatment of ACLF patients,risk factors including low Alb,low PLT,upper gastrointestinal bleeding,and pulmonary infection should be prevented,and early diagnosis and intervention of these risk factors helps to reduce the incidence of SBP.