<p>This study aimed to investigate the distribution characteristics, resistance mechanisms, and transmission dynamics of multidrug-resistant <i>Acinetobacter baumannii</i> (MDRAB) in the ICU of a hospital in China. A total of 272 clinical MDRAB isolates were collected from the ICU of a single hospital between 2013 and 2025. Resistance genes associated with β-lactams, carbapenems, and aminoglycosides were detected, and antimicrobial susceptibility testing was performed to assess resistance phenotypes. Molecular typing, including sequence typing (ST) and pulsed-field gel electrophoresis (PFGE), was conducted on selected patient and environmental isolates to further analyze in-hospital transmission patterns. Of the 272 isolates, approximately 53% were derived from respiratory specimens. All isolates exhibited 100% resistance to carbapenems, which was consistent with the universal presence of the <i>bla</i>_{<i>OXA−23</i>} gene. Environmental surveillance revealed a high isolation rate of <i>A. baumannii</i> in areas surrounding infected patients, particularly those with respiratory infections.&#xa0;PFGE analysis showed that some environmental isolates exhibited different patterns from the corresponding clinical strains, suggesting potential microevolution and involvement in the ongoing in-hospital dissemination of MDRAB. This study systematically analyzed the resistance characteristics and transmission patterns of 272 MDRAB isolates collected from a hospital ICU in China between 2013 and 2025. The results of the study showed that <i>bla</i>_{<i>OXA−23</i>} may play an important role in carbapenem resistance. Both clinical and environmental isolates exhibited multidrug resistance and the ability to persist in hospital environments. PFGE analysis indicated possible microevolution among environmental strains, potentially facilitating the sustained transmission of MDRAB within the hospital setting.</p>