The physical and optical properties of ion-assisted deposited ZnS films with different ion beam densities are investigated. The study results show that the phenomenon of inhomogeneous growth of ZnS films happens during the ion-assisted deposition. The inhomogeneity and refractive index of ZnS films increase with the increase of ion beam density, and the crystallization degree of films also increases. The inhomogeneity of films causes more difficulties for the preparation and design of films, especially an uncertainty for the preparation of a multilayer film system. The results provide an important reference for the development and production of infrared optical ZnS films.