Objective To analyze the epidemiology and change in antimicrobial resistance of clinically isolated pathogens causing intra-abdominal infection(IAI) in intensive care unit (ICU), and provide reference for clinicians to manage intra-abdominal infection and optimize the initial empirical anti-infection treatment. Methods IAI cases in department of critical care medicine of Nanfang Hospital from January 2011 to December 2018 were retrospectively analyzed. Two research periods were divided (the former 4 years and later 4 years), distribution of IAI bacterial flora and change in antimicrobial resistance of two periods were compared and analyzed. Results A total of 522 patients with IAI were investigated, 431 patients (181 in the former period and 250 in the later period) were finally included, a total of 527 strains of pathogens causing IAI were isolated. Epidemiological characteristics and antimicrobial resistance of isolated strains from patients with IAI were as follows: The proportions of Gram-negative bacteria, Gram-positive bacteria and fungi were 48.2%, 34.0% and 17.8% respectively; the top 5 strains were Escherichia coli, Enterococcus faecium, Klebsiella pneumoniae, Candida albicans and Enterococcus faecalis, accounting for 63.0% of all isolates; isolation rate of ESBLs-producing strains of Escherichia coli decreased in the later period than the former period (68.1% vs 45.9%, χ²=5.291, P=0.021), susceptibility rates to cephalosporins and piperacillin/tazobactam increased, resistance rate to carbapenem antibiotics remained at a low level and unchanged; isolation rate of ESBLs-producing strains of Klebsiella pneumoniae didn't change (28.6% vs 23.1%, χ²=0.212, P=0.645), but rate of carbapenem-resistant Klebsiella pneumoniae increased (14.3% vs 38.5%, χ²=4.103, P=0.043), antimicrobial susceptibility rates generally showed a downward trend; Acinetobacter baumannii was one of the most common non-fermentative bacteria, pandrug resistance was serious in the former period, resistance rate to imipenem and meropenem was 100%, and susceptibility rate was about 50% in the later period; vancomycin-resis-tant Enterococcus faecium and Enterococcus faecalis were not found, there was no significant change in resistance rate between the former and later periods. Conclusion Gram-negative bacteria are the main pathogens causing adult IAI. Although ESBLs-producing Enterobacterales and pandrug-resistant Acinetobacter baumannii are controlled to a certain extent, carbapenem-resistant Klebsiella pneumoniae is increasing gradually, antimicrobial resistance situation is still not optimistic, surveillance on epidemiology and antimicrobial resistance trend of pathogens causing IAI still need to be continued.