Terahertz (THz) radiation lies between the infrared and microwave regions of the electromagnetic spectrum. Because of organisms’ unique response to the THz wave, THz wave applications in biomedical research, especially in its interactions with biological tissues become a hot spot. Whether the THz wave has the photodynamic effect by exciting the photosensitizer is explored in the study. The wide spectrum (1-3 THz) of pulse terahertz is used as a light source to excite the photosensitizer-hematoporphyrin monomethyl ether (HMME) for 30 min, and then DPBF is used as singlet oxygen scavenger to test the yield of singlet oxygen. HepG2 cells in conventional culture are illuminated with the same dose of terahertz wave, the cell morphology is observed by an optical microscope, the cell activity is determined by MTT method. The singlet oxygen production in PS+THz group is significantly higher than that of pure THz wave irradiation (21.04% vs. 2.39%). Compared to control cells, HepG2 cells in PS+THz group are slightly rounded and have a tendency to shrink. The activity of HepG2 cells incubated in HMME (HMME+THz group) is reduced to 81.13% after irradiation by THz wave (99.21% in THz group). The experimental results show that the THz wave of wide spectrum (1-3 THz) and nanojoule energy can excite the photosensitizer of HMME with excitation efficiency of about 20%.