More and more ceftazidime-avibactam-resistant KPC-producing Klebsiella pneumoniae have been reported with its widespread use, and the detection rate of KPC variants has increased dramatically. However, the evolutionary mechanism and fitness effects during KPC mutation remained unknown. Here, we report the complex in vivo evolutionary trajectories of two novel KPC variants, KPC-155 (L169P/GT242A) and KPC-185 (D179Y/GT242A), from K. pneumoniae in the same patient. The novel variants were shown to confer ceftazidime-avibactam resistance but restore carbapenem susceptibility based on the results of plasmid transformation assays, cloning experiments, and enzyme kinetic measurements. In vitro, competition experiments highlighted the adaptive advantage conferred by strains carrying these KPC variants, which could lead to the rapid spread of these ceftazidime-avibactam-resistant strains. The growth curve indicated that bla KPC-185 had better growth conditions at lower avibactam concentration compared to bla KPC-155 , which was consistent with ceftazidime-avibactam use in vivo. In addition, replicative transposition of the IS26-flanked translocatable unit (IS26-ISKpn6-bla KPC -ISKpn27-IS26) also contributes to the bla KPC amplification and formation of two copies (bla KPC-2 and bla KPC-185 ), conferring both carbapenem and ceftazidime-avibactam resistance. However, strains with double copies showed reduced competitive advantage and configuration stability. The comparative plasmid analysis of IS26 group (IS26-bla KPC -IS26) and Tn1721 group (Tn1721-bla KPC -IS26) revealed that IS26-insertion could influence the distribution of resistance genes and ability of self-conjugation. The dynamic changes in bla KPC configuration highlight the need for consistent monitoring including antimicrobial susceptibility testing and determination of bla KPC subtypes - during clinical treatment, especially when ceftazidime-avibactam is administered.