N doped TiO2 films were deposited in direct current pulsed magnetron sputtering system at room temperature. We have studied the influence of O2 flow rate on the crystal structure of deposited films by using stylus profilometer, X-ray photoelectron spectroscope, X-ray diffractometer, and ultraviolet-visible spectrophotometer. The results indicate that the growth behavior and crystal structure of N doped TiO2 film is dominated by the O2 flow rate. It was found that the chemical stiochiometry is close to TiO1.68±0.06N0.11±0.01 for all film samples, in which the N mainly exists in substitutional doped state. When O2 flow rate is 2 sccm (1 sccm=1 mL/min), N doped TiO2 film has amorphous structure with high growth rate, which contains both anatase phase and rutile phase crystal nucleuses. In this case, the film displays the mix-phase of anatase and rutile and the band gap is 2.86eV after annealing treatment. The film growth rate decreases with increasing O2 flow rate. After annealing treatment, the band gap of N doped TiO2 films decreases with increasing O2 flow rate. While N doped TiO2 film is anatase phase when O2 flow rate is 12sccm. In this case, the band gap is 3.2eV after annealing treatment. It should be noticed that no TiN phase appears for all samples before and after annealing treatment.