Based on the principle of electronegativity, a reasonable infrared spectrum model is built, and the relationship between the vibration frequency of TiO2 infrared spectrum and the electronegativity of element is investigated. (Fe, N) codoped TiO2 samples were prepared with the sol-gel method. The crystalline phase and IR spectra of the samples were characterized with X-ray diffraction and Fourier infrared spectroscopy (FTIR). XRD phase analysis shows that amorphous structure of TiO2 samples are mainly transformed into anatase structure when the calcination temperature is 600 ℃. As the calcination temperature is increasing, the X-ray diffraction peaks of TiO2 gradually become narrower, with greater intensity, and gradually increasing crystallinity of TiO2. When the calcination temperature is 700 ℃, the diffraction peaks of anatase disappear, only the diffraction peaks of rutile phase can be observed. infrared spectrum indicate that there exists a wider absorption peak in the range of 650～500 cm-1 for (Fe,N) Codoped TiO2. Stretching vibration frequency of (Fe, N) Codoped TiO2 infrared spectra, Fe and N doped location, molecular structure and bond valence feature are obtained by the principle of electronegativity. Firstly, the reduced mass μ is computed. Then according to the relationship between classical mechanics stretching force constant k and frequency ν, molecular vibration frequency of doped rutile or anatase TiO2 with the same oxygen octahedron structure unit via combining with the relationship between the force constant and the electrical negative, the calculation of bond order. The results show that the (Fe, N) Codoped TiO2 infrared spectrum calculated by the principle of electronegativity is in agreement with the stretching vibration frequency by the experimental measurement.