The work aims to study the relevant structure and performances of composite film, with chitosan and corn starch as the main film-forming substrate and the nano ZnO as the additive. The chitosan liquid, starch gelatinized liquid and nano ZnO were homogeneously mixed by solution blending process and then film casting was done. The influence of the mass ratio of chitosan/starch and the nano ZnO content on the mechanical properties and water vapor permeability of the composite films was analyzed, and the relevant structure of the composite films were characterized by infrared spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermogravimetry analysis (TGA). When the mass ratio of chitosan/starch was 1∶1, and the mass fraction of nano ZnO was 9%, the composite films obtained had better performance in their respective systems. These results pointed out that there was a good compatibility between chitosan and starch. The addition of nano ZnO can improve the mechanical properties of composite films, reduce their water vapor permeability and improve their thermal stability.