C-doped Ti–O films with different titanium suboxide contents are prepared by DC magnetron sputtering deposition at different sputtering powers. The films with different phases are formed after annealing at 873[Formula: see text]K in air. The structure of the films is characterized by X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy. The optical properties and surface roughness of the films are investigated by UV–vis spectroscopy and atomic force microscopy, respectively. Photocatalytic activity of the thin films is studied by degrading the methyl orange solution under xenon lamp (300[Formula: see text]W) irradiation. The results show that the C-doped Ti–O thin films with higher titanium suboxide contents ([Formula: see text]%) tend to form the rutile phase after annealing, whereas the films with a lower titanate content ([Formula: see text]%) are easy to form anatase phase by annealing.