Objective To investigate the in vivo and in vitro antimicrobial activity of ceftazidime/avibactam (CZA) alone or in combination with aztreonam (ATM) against carbapenem-resistant Enterobacterales (CRE), and provide evidence for clinical anti-infective therapy. Methods The minimum inhibitory concentrations (MICs) of CZA and ATM against 52 clinically isolated non-repetitive CRE strains in a hospital from 2018 to 2022 were determined with microbroth dilution method, and the combined antimicrobial susceptibility testing was performed with the chessboard dilution method. Time-killing curve and Galleria mellonella infection model were used to test the bactericidal effect of CZA alone or in combination with ATM. Results Among the 23 KPC-producing CRE strains, 91.3% (n=21) had MIC ≤4 μg/mL for CZA, and 8.7% (n=2) had MIC ≥128 μg/mL for CZA. MIC of CZA to 29 CRE strains (strains producing NDM, IMP, KPC+IMP, and KPC+NDM) were all ≥128 μg/mL. Of the 31 CZA-resistant strains, 93.5% (n=29) strains had fractional inhibitory concentration (FIC) <0.5 for combination of CZA and ATM, while 6.5% (n=2) had FIC of 0-1. The time-killing curve showed that CZA had bactericidal effect on KPC-producing strains, and CZA combined with ATM had bactericidal effect on CZA-resistant strains. Compared with the monotherapy group, CZA combined with ATM treatment significantly improved the survival rate of CRE-infected Galleria mellonella (median survival time 120 hour, P=0.001). Conclusion CZA has good antimicrobial activity against KPC-producing bacteria. The combination of CZA and ATM had synergistic bacteriostatic effect on CZA-resistant strains.