The invention discloses novel application of a di-perylene bisimide compound used as a photosensitizer, wherein the di-perylene bisimide compound is shown in a formula I. The inventor considers the property of the di-perylene bisimide as the photosensitizer from four following aspects of: 1, detecting the generation of singlet oxygen; 2, detecting time evolution trends of the triplet of a singlet oxygen precursor DiPBI respectively in aerobic condition and anaerobic condition; 3, quantitatively measuring relative quantum yield of the singlet oxygen generated by the DiPBI compound; and 4, inspecting the photostability of the DiPBI compound. Tests prove that the di-perylene bisimide compound has excellent photoactivating capability, and presents better photostability, can durably develop photoactivating function. Thus, compared with other photosensitizers (such as porphyrins, methylthionine chloride and the like), with remarkable advantages, the di-perylene bisimide compound has wide application prospect.