In order to improve electrochromic properties of tungsten-oxide (WO3) thin films, polyethylene glycol (PEG)-doping WO3 films are prepared by peroxopolytungstic acid sol-gel method. Microstructure, optical and electrochromic properties of the films are investigated by X-ray diffraction, spectral ellipsmetry, ultraviolet-visible spectrophotometer and cyclic voltammetry, respectively. Results show that PEG-doping tungsten-oxide films contain nanocrystalline/amorphous nanostructure, which facilitate ions transport in the films. Compared to pure WO3 film, the PEG-WO3 film possesses wider spectral modulation, higher coloring efficiency, good electrochromic reversibility and cyclic stability.