Objective To investigate the impact of respiratory colonization of carbapenem-resistant Acinetobacter baumannii (CRAB) on 28-day mortality of patients with severe/critical coronavirus disease 2019 (COVID-19) in intensive care unit (ICU). Methods Clinical data were collected from severe/critical COVID-19 patients admitted to general ICU and respiratory ICU in a tertiary Chinese medicine hospital from December 9, 2022 to December 9, 2023. According to the detection results of CRAB from sputum culture during ICU stay, patients were divided into respiratory CRAB colonization group and non-CRAB colonization group. Kaplan-Meier survival curve was plotted to compare the 28-day mortality between two groups of patients after ICU admission. Relationship between respiratory CRAB colonization and 28-day mortality was explored by Cox proportional hazards model, and subgroup analysis was performed. Results A total of 88 patients with severe/critical COVID-19 were included in analysis, out of which 27 had respiratory CRAB colonization (CRAB colonization group) and 61 didn’t have respiratory CRAB colonization (non-CRAB colonization group); 37 patients (42.0%) died within 28 days after admission to the ICU. Kaplan-Meier survival curve showed that the 28-day mortality in CRAB group was higher than that in non-CRAB group (66.7% vs 31.1%, P<0.001). Cox univariate analysis showed that the 28-day mortality risk of patients in the CRAB colonization group was 2.91 folds of those in the non-CRAB colonization group (HR=2.91, 95%CI: 1.52 -5.58; P<0.05). After covariates adjusting for age, sex, underlying diseases, white blood cell count, neutrophil-to-lymphocyte ratio, hypersensitive C-reactive protein, respiratory frequency, oxygenation index, lactate dehydrogenase, urea nitrogen, creatinine, lactic acid, and D-dimer, the risk of death in the CRAB colonization group was still higher than that in the non-CRAB colonization group (HR=2.54, 95%CI: 1.15-5.58; P<0.05). Subgroup analysis showed that respiratory CRAB colonization and 28-day mortality in severe/critical COVID-19 ICU patients was affected by gender, serum albumin, creatinine, and D-dimer levels (interaction P<0.05 for all). Conclusion The short-term mortality of severe/critical COVID-19 patients in the ICU increases significantly after secondary colonization of respiratory CRAB. Effective prevention and control of colonization and infection by multidrug-resistant organisms are crucial for ensuring patient prognosis.