For the purpose of studying the optical constants of CsPbBr3 films prepared by the multi-step spin coating method, CsPbBr3 films were prepared on silicon and SnO2∶F (FTO) substrates by the multi-step spin-coating with lead bromide and cesium bromide as raw materials. The ellipsometric spectrum of films on silicon substrate was achieved by a photoelastic modulating ellipsometry spectrometer. The parameters of the ellipsometric spectrum were fitted by using the combination model of Tanguy and Tauc-Lorentz three oscillators, and the dispersion relationship of the optical constants of thin films in the range of 1.00 eV~5.00 eV was obtained. Fluorescence emission spectra and absorption spectra were used to verify the ellipsometry fitting results. The results show that the optical constants of CsPbBr3 films prepared by the multi-step spin coating method are different from those of other methods, and the refractive index may be negatively correlated with the surface roughness of the films. The band gap obtained by ellipsometry fitting is 2.3 eV, which verifies the results of fluorescence spectra and absorption spectra. This study provides a reference for the fitting analysis of the ellipsometry spectra of CsPbBr3 films prepared by multi-step spin coating.