Anew kind of photochromic composite film is prepared by depositing gold nanoparticles onto the surface of MoO3 thin film. It is found that gold nanoparticles can improve the UV-light coloration performance of the MoO3 thin film. X-ray photoelectron spectroscopy and surface photovoltage spectroscopy measurements indicate that more water is adsorbed on the composite film surface after the deposition of gold nanoparticles. The increase in the adsorbed water on the film surface allows an efficient utilization of the photogenerated holes during the coloration process. Specifically, the Schottky barrier formed at the MoO3/Au interface facilitates the separation of photogenerated carriers. As a result, the photochromic performance of the MoO3 film is enhanced greatly by the gold nanoparticles.