We found in our previous work that the high photoactivity of N-doped TiO2 for the oxidation of propylene under visible light was attributed to the photoactive center Vo-NO-Ti and the formation of sub-band originated from a large amount of single-electron-trapped oxygen vacancies (denoted as Vo; C. X. Feng, Y. Wang, Z. S. Jin, J. W. Zhang, S. L. Zhang, Z. S. Wu, Z. J. Zhang [2008], New J. Chem. 32, 1038). In the present study, the structure of the sub-band within Eg of a representative sample N-NTA-400 was investigated by means of photoluminescence (PL) spectrometry and ultraviolet-visible light-near infrared diffuse reflectance spectra. The coaction of the sub-band and doped nitrogen on visible light photocatalytic activity of N-doped TiO2 was also investigated. The electron spin resonance spectra measured under laser irradiation (λ = 532 nm) indicate that the doped nitrogen may contribute to stabilize the trapping electron center, i.e. surface oxygen vacancy (Vo••), and hence suppress the PL, enhancing the photocatalytic activity.