Gold nanoparticles synthesized by the chemical reduction of hydrogen tetrachloroaurate were used to modify the surface of vacuum evaporated WO3 thin films through a spin coating technique. It was found that the gold nanoparticles could improve the electrochromic performance of the WO3 film greatly. The experimental results indicated that the conductivity of the thin film was increased after the surface modification. In addition, it was found that the composite thin film could show a better electrochromic performance in aqueous acid system than in organic solution.