In order to analyze the optical constants of the TiO2 thin film prepared by the sol-gel method, multi-layer TiO2 thin films were prepared by spin-coating, and the surface morphology was analyzed by scanning electron microscopy. The refractive index dispersion and porosity of the film were analyzed by ellipsometry. The fitting analysis was carried out, and the fitting results were verified by in-situ common-angle reflectance spectroscopy. The TiO2 thin film thickness, porosity, and refractive index dispersion curves were then obtained. The results show that the thickness of the TiO2 thin film has a linear relationship with the number of spin coatings. The porosity of the film is about 15% and has nothing to do with the number of spin coatings. The New Amorphous dispersion model can fit the ellipsometric spectrum of TiO2 thin film prepared by the sol-gel spin coating method in the 1.55eV~4.00eV band. This study provides a reference for the measurement of the optical constants of the TiO2 thin film prepared by the sol-gel method.