Nitrogen and sulfur doped titanium dioxide photocatalysts were prepared by the sol-gel method.The products were characterized by X-ray diffraction(XRD),transmission electron microscopy(TEM),and UV-visible diffuse reflectance spectra(DRS).Photocatalytic activities of the samples were investigated on the degradation of methyl orange(MO).The effect of the dopants on the electronic structure of TiO2 was studied by the first-principles calculations based on the density functional theory(DFT).The orbital hybridization resulted in energy gap narrowing and electronic delocalization in the crystal of doped TiO2.Mobile electrons of varied energetic states could offer enhanced electron transfer,together with optical absorption improvement.The results show that the doping elements of N and S play a cooperative role in the modification of elecconic structure,which enhances the photocatalytic performance.The experimentally observed absorption edges of N-doped TiO2,S-doped TiO2,and N,S-codoped TiO2 are 420,413,and 429 nm,respectively,which can be explained by the theoretical calculation results.