摘要： The power conversion efficiency of perovskite solar cells (PSCs) has jumped over 23%. However, the stability of perovskites is still a major obstacle for its commercialization. In order to explore the optical degradation process of perovskite materials, the spectrometric ellipsometry (SE) was used to study the optical properties change of perovskite film caused by degradation. Humidity is the main degradation factor to be considered. First, the CH3NH3PbI3 perovskite thin films were prepared on sapphire substrate by one-step spin coating method. Second, SE was used to obtain the spectral response curves with wavelength-range from 210 nm to 1690 nm. Perovskite films were measured a few times at 65° incident angle under ambient condition (Temperature:21°C; Relative Humidity:80%)by SE. Then, the optical models of the films were modelled by Tauc-Lorentz model and the measured curves were fitted to obtain the changes of optical constants with degradation. As a result, when the wavelength is less than 700nm, the spectral curves of CH3NH3PbI3 gradually descend but ascend with the wavelength when the wavelength is more than 700nm after 30 days. The experimental results show that spectrometric ellipsometry can reflect the changes in optical characteristics during the degradation of perovskite thin films. Analysing the change of the optical properties can help reveal the degradation mechanism of perovskite materials.