Over the last decade, there has been great interest in electrochromic technology for smart windows. Various kinds of electrochromic materials were examined and their electrochromic processes were analyzed in terms of optical and electrochemical properties. For glazing applications, there are still two systems: one is all solid state whilst the other is a laminated system that utilizes an organic electrolyte. The response of an electrochromic system is a complicated function of the sheet resistance of ITO, and the ionic transport of the electrolyte, charge storage layer and electrochromic film. In this paper, analysis of electrochromic process is focused on the ionic transport in the electrochromic thin films using finite diffusion model.