The influence of Ag doping ratio on the antibacterial properties of CoP/CNx composite photocatalysts was studied from dual perspectives: photocatalyst structure-activity relationships and bacterial response mechanisms. Ag/CoP/CNx composite materials were fabricated using the photodeposition method. The crystal structure, morphology and optical properties were systematically characterized through X-ray diffraction, transmission electron microscopy, and UV-visible diffuse reflectance spectroscopy. The separation efficiency of photogenerated carriers was enhanced when Ag was introduced, which resulted in improved photocatalytic activity. Complete E. coli inactivation was accomplished within 20minutes when 2wt% Ag doping was employed with an initial bacterial concentration of 10⁴CFU/mL. The bactericidal efficiency was sustained at 100%, 99.99%, 98.60%, and 97.51% over four successive cycles, whereby remarkable stability was demonstrated. Through free radical quenching experiments, holes (h⁺) were determined to be the dominant active species, while superoxide radicals (·O₂^-) were identified as secondary active species. The sterilization efficiency was decreased to 71.9% and 23.7% after radical scavenger were introduced, respectively. The K⁺ release concentration was elevated from 2.64mg/L to 5.47mg/L (CoP/CNx) and 7.30mg/L (Ag-CoP/CNx). The destruction of cell membrane structures was verified by scanning electron microscopy and Fourier transform infrared spectroscopy analyses. This damage was induced by holes and superoxide radicals, whereby intracellular contents were leaked. Cell penetration was subsequently observed, oxidative damage to biomolecules, including DNA and proteins, was triggered. The research findings were established as theoretical and technical foundations for the implementation of Ag-based nanocomposite photocatalysts in wastewater treatment and environmental disinfection applications.