Online low emissivity glass (Low-E glass) is a promising glass product. Simulation of the spectra and determination of the optical constants of online Low-E glass are of practical interest for many applications such as product design, adjustment of coating process and comparison of samples produced using different methods. The online Low-E glass investigated here has two layers of films on 6 mm thick float glass substrate, which include the functional layer (the upper layer) and the transition layer (the lower layer). In this paper, the relation between transmittance and the parameters used in the model in the visible and near-infrared region was derived, so was the relation between reflectance and the parameters used in the model in the infrared region. The parameters used in the model were obtained by fitting the measured and simulated spectra. From the obtained parameters, the optical constants of the functional layer of online Low-E glass in the visible region and the infrared region were obtained, respectively. The sheet resistance and the infrared reflectance of Low-E glass were also calculated from the obtained fitting parameters. The simulated results are well consistent with the experimental ones. (C) 2008 Elsevier B.V. All rights reserved.