Abstract: Polyurethane (PU) is widely used in the field of biomedical implants due to its tailorable mechanical properties, excellent processability and good biocompatibility. However, planktonic bacteria often adhere to the surfaces of PU implants, which may cause infections and threaten patient health. Therefore, the development of polyurethane materials with high antibacterial efficiency has significant research value. Using bromomethyl alkyl acid as the raw material, three quaternary ammonium salt (QAS) chain extenders Bn (n=1, 3, 5) with different alkyl arm lengths were synthesized by introducing QAS groups and dihydroxyl structures, and regulating the alkyl arm lengths between the bromine atoms and ester groups in bromomethyl alkyl acid (1, 3, 5 carbon atoms, respectively). After the pre-polymerization of polycaprolactone diol (PCL2000) with hexamethylene diisocyanate (HDI), a co-extension chains reaction was carried out using 1,4-butanediol (BDO) and Bn to prepare polyurethane (PU-Bn) with adjustable alkyl arm lengths between the QAS cation center and the main chain. The influence of the QAS arm length on the thermodynamic properties, antibacterial properties and hemolytic properties of the material was systematically studied. The results show that all PU-Bn materials exhibit good thermal stability, excellent mechanical properties and a low hemolysis rate. The antibacterial experiment reveals that the QAS arm length has a significant impact on the antibacterial performance. Polyurethane with a shorter arm length demonstrates better antibacterial ability, and the antibacterial effect follows the order: PU-B1 > PU-B3 > PU-B5.