Objective To investigate the causes of healthcare-associated infection(HAI) outbreak caused by extensively drug-resistant Acinetobacter baumannii (XDR-AB) in intensive care unit (ICU) of a hospital, and find out the sources and routes of transmission, so as to provide evidence for the prevention and control of HAI. Methods Epidemiological investigation of patients with XDR-AB infection and environmental hygiene monitoring on ICU of a hospital from January to February 2018 were carried out, comprehensive measures were taken to control the outbreak. Results XDR-AB infection occurred in 10 patients in ICU in a short period of time, antimicrobial susceptibi-lity testing results of AB isolated from B08, C08 and A02 beds were the same, which was a suspected clone, antimicrobial susceptibility testing results of AB isolated from C09, B09 and A03 beds were the same, which was another suspected clone. Through environmental hygiene monitoring, similar AB clones were isolated from the specimens of infusion pump, bedside table, bedside rail, infusion tower, nursing table, monitor, rack for hand disinfectant, equipment tower, hand-operated handle at the end of bed, and health care workers' paraphernalia. No new XDR-AB infection occurred after comprehensive control measures were taken, no drug-resistant AB was isolated from environment and health care workers' hands on March 5. Conclusion Poor hand hygiene of health care workers and incomplete environmental disinfection in ICU are the main causes for the outbreak of HAI.