The vitro photodynamic therapy(PDT) inactivation efficiency of HL60 cells based on cadmium selenide-doped titanium dioxide nanoparticles modified by folic acid (FA-CdSe-TiO2) is investigated and the mechanism of folic acid modification to enhance the PDT effect of CdSe-TiO2 nanoparticles is discussed. The CdSe-TiO2 nanoparticles are prepared by hydrolysis deposition method, and FA-CdSe-TiO2 nanoparticles are prepared by surface modification method. The structure and optical properties of the nanoparticles are characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), ultraviolet visible absorption spectrum and so on. The cell viability is measured by CCK-8 method. The intracellular reactive oxygen species (ROS) levels are analyzed by fluorescence probe labeling technique, and the ultrastructure of the cells is observed by scanning electron microscopy. The results show that FA-CdSe-TiO2 nanoparticles have no significant change in cytotoxicity compared with CdSe-TiO2 nanoparticles in the darkroom condition. However，under the light condition, FA-CdSe-TiO2 has a great increase in cell growth inhibition rate. When the ratio of folic acid is 1.0, the PDT efficiency is 84% at 18 J/cm2 light irradiation. Folic acid surface modification increases the uptake efficiency of HL60 cells to the nanoparticles, and the level of ROS in the cells is increased, thereby the PDT inactivation efficiency of HL60 cells is enhanced.