The preparation precedures of the WO3 electrochromic thin film and the semi-solid state WO3/LiClO4+PC/TiO2 electrochromic device are studied. The cyclic voltammogram characterization of WO3 thin film and electrochromic device (ECD) with different scan potentials and scanning rates are investigated. The coloration efficiency of WO3 film in 1 M/L LiClO4+PC is obtained. The results show that the sol-gel process is an effective method to prepare the large-area electrochromic smart windows.