The photocatalytic inactivation efficiency of HL60 cells in vitro based on cadmium sulfidedoped titanium dioxide modified folic acid (FA-CdS-TiO₂ ) and the mechanism of folic acid enhancing the effect of CdS-TiO₂ on PDT were researched in this paper. The FA-CdS-TiO₂ nanoparticles were prepared by surface modification method.The nanoparticles were characterized using transmission electron microscopy (TEM), fourier transform infrared spectroscopy(FTIR), fluorescence excitation spectroscopy(FS).Cell viability was measured by CCK8 method.The intracellular reactive oxygen species (ROS) and the uptake efficiency of nanoparticles were analyzed by fluorescence probe labeling technique. The results showed that the size and optical properties of  nanoparticles after folic acid modification met the requirements of photosensitizer, and the naoparticles don’t cause new cytotoxicity. After folic acid modification, the uptake efficiency of nanoparticles by cells was enhanced, the production of ROS in cells increased, and the PDT efficiency of FA-CdS-TiO₂ nanoparticles increased significantly.When the concentration of FA-CdS-TiO₂was 20 μg/mL, the cell survival rate is about 85% under darkroom conditions, the inactivation rate reached 78% under visible light,which indicates that the higher PDT inactivation efficiency under lower dark toxicity is achieved.