ObjectiveTo evaluate the causes of nosocomial infection cluster cases(NICC) caused by drugresistant Acinetobacter baumannii(DRAb). MethodsClinical data and epidemiological survey results of 4 NICC were analyzed and described by statistics.ResultsFourteen cases in 4  DRAb NICC occurred at ICU  in hot weather season; 10(71.43%) were critical patients; 6(42.86%) were older patients (>65 years); the median time of ICU stay were 8 days; the local physiological barriers of all cases were destroyed before developing DRAb infection.12 cases (85.71%) developed pulmonary infection (64.29% for ventilatorassociated pneumonia); 11(78.57%) were infected with pandrug resistant Acinetobacter baumannii (PDRAb). Nine patients (64.29%)  had a history of longterm use of combination  antimicrobial agents before developing NI; 2 NICC  were afferent NI.ConclusionThe occurrence  of ICU DRAb  NICC is  associated with susceptibility of patients, isolation and disinfection, ward NI surveillance, use of antimicrobial agents, and biological characteristics of  Acinetobacter baumannii