Based on the optical mechanism of online Low-E glass,the optical constants of functional layer and transition layer of online Low-E glass in visible-near infrared region were analyzed by the spectroscopic ellipsometry.The ellipsometric data of the sample at three different angles of incidence were measured at first,then the Lorentz two-oscillator model and Cauchy model were used to characterize the dispersion characteristics of functional layer and transition layer of online Low-E glass ,respectively.The optical constants and the thickness of each layer of online Low-E glass were obtained by fitting the measured ellipsometric data.Moreover,the Scanning Electron Microscope (SEM) were used to investigate the film thickness of the sample.The fitting results suggest that Lorentz two-oscillator model and Cauchy model can explain the optical properties of online Low-E glass well.Meanwhile,the ellipsometry also provides a reliable method for the determination of optical constants and thickness of the multilayer film systems.