Abstract: OBJECTIVE To investigate the cause of suspected outbreak of nosocomial infection of carbapenem-resistant Acinetobacter baumannii(CRAB) in patients with severe COVID-19 infection in the intensive care unit (ICU) and to analyze the risk factors for the event. METHODS Epidemiological investigation and environmental hygiene detection were conducted on eight patients with CRAB infection in the ICU of the Affiliated Hospital of Inner Mongolia Medical University from Jan 12 to Jan 31 in 2023, and the corresponding intervention measures were taken. RESULTS CRAB infection occurred in eight severe cases of COVID-19 in ICU in a short period of time. Epidemiological investigation showed that all the above patients were COVID-19 infected patients with serious basic conditions, and the problems including overlapping hospital stays,insufficient bed sheet area, overlapping nursing workers, new cleaning staff and non-standard cleaning and disinfection of surfaces existed. In the investigation of environmental microorganisms, a total of 65 specimens were collected from the environmental surfaces and hands of healthcare workers. CRAB was detected in three samples, with a detection rate of 4.62% (3/65). The abnormal sites were patient bed rails, monitor panels and nutrition pumps, in which the sensitivity results were basically consistent with eight strains of CRAB detected in patients. After taking intervention measures such as suspending the treatment of patients, strengthening the training of prevention and control of multi-drug resistant bacteria, standardizing the hand hygiene of staff, and strengthening the implementation of disinfection and isolation, the incident was effectively controlled. CONCLUSION The emergency capacity expansion and transformation of COVID-19 intensive care unit (ICU), unreasonable layout process, incomplete cleaning and disinfection of environmental surface, and inadequate implementation of contact isolation measures for medical personnel infected with CRAB may be the main reasons for the outbreak of nosocomial infection of CRAB.