The interface potential of WO3 film and lMLiClO4- PC solution and its measurement are discussed. Three kinds of WO3 films with different electrochromism proPerties were made, and their variation of the interface potentials were measured as a function of the number of Li + ions injected into WO3 film. It is found that the limited maximum number of injected Li+ ions is predicable through the variation trendaney of interface potential. The best deposition parameters of thermal evaporation for electrochromic WO3 film are obtained.