Nitrogen-doped modified TiO2 films were prepared through sol-gel method. The thickness, surface microstructure and composition were analyzed by nano indenter, scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of N-doped TiO2 films was researched through the degradation experiment of methylene blue under UV light. Results showed that nitrogen ions are doped into TiO2 films by adding urea and they are between TiO2 crystal lattices and mainly in interstitial configuration and substitution configuration. The films are very flat with the thickness of between 50-200 nm. Nitrogen ions doping improves the photocatalytic activity of TiO2 films. When N/Ti=0.015 (atom ratio) in TiO2 films, it takes single N-doped TiO2 film 2.5 h to decompose the methylene blue solution.