By the magnetron sputtering method, the tungsten oxide (WO3) films are prepared under different working pressures. The regulating effect of working pressure on WO3 film microstructure is studied, and the effect of WO3 film microstructure on its electrochromic performance is also investigated. The study results show that the prepared WO3 film is with an amorphous phase and its surface presents a peak-shaped structure. With the increase of working pressure, the WO3 film microstructure becomes loose, and the electrochromic response time and the cycle lifetime are shorten. Under the optimal film microstructure condition, the optical density of WO3 films is 0.64 and the cycle lifetime is up to 1500 cycles.