The work aims to study performance degradation mechanism of WO3 film in ITO/WO3/LiTaO3/NiOx/Al reflective inorganic all-solid-state films at high temperature. Electrochromic device and WO3 monolayer film were deposited in the method of DC magnetron sputtering and heated at high temperature. Reflectance variations of the electrochromic device were tested. Microstructure and electrochemical cycle performance of WO3 film were analyzed. The reflectance variation decreased little at temperature below 350 ℃, and decreased obviously at the temperature over 350 ℃. WO3 film transformed from amorphous to crystal structure. The electrochemical cycle characteristic showed that the electrochromic response time extended as heating temperature increased, response time soared and electrochromic property degenerated at the temperature below 350 ℃ while electrochromic stability increased. The porous amorphous structure of WO3 film can provide more injection and transmission routes for ions, electrochromic property is better while cycling stability of porous amorphous structure is worse. Electrochromic property of compact crystal structure is worse since routes are closed and ions (electrons) cannot be injected or transmitted easily, but its cycling stability is better.