In this study, we prepared polymer quaternary ammonium salt-capped silver nanoparticles (PQAS-AgNPs) and investigated their antimicrobial activities. The antimicrobial effectiveness of PQAS-AgNPs on (), and the effect of dose, pH, chloride ion and humic acid (HA) were studied. It was found that PQAS-AgNPs revealed excellent antimicrobial activity to , compared with polyvinylpyrrolidone-capped silver nanoparticles (PVP-AgNPs), which was the reference antimicrobial material. The positive surface, the antimicrobial activity of PQAS, and the synergistic antibacterial effect between PQAS and AgNPs contributed to the significant antibacterial superiority of PQAS-AgNPs. This study demonstrated that the impact of the dose of the material was positive and the microbiocidal efficacy of PQAS-AgNPs was stronger at lower pH. In addition, the antibacterial performance of PQAS-AgNPs decreased in the presence of Cl and HA. Finally, in combination with the results of FCM and adenosine triphosphate (ATP) content, it was found that PQAS-AgNPs destroyed the respiratory chain of bacterial cells, reduced the synthesis of ATP, and destroyed the cell wall and cell membrane function.