Ir is an important vacuum-ultraviolet (VUV) reflecting material, and has various applications in hi-tech fields including solar physics, cosmic physics, life science, and synchrotron radiation. The reflective performance of Ir film in the VUV wavelength region was studied theoretically and experimentally. Based on the theoretical model of single metal layer on absorbing substrate, the optimum calculation was performed for Ir layer of various thickness on K9 glass and quartz substrate in the VUV wavelength region. Considering the calculation results and previous research, single layer Ir films of different thickness were fabricated on K9 glass and quartz substrate by electron gun evaporation system, and nearly 30％ normal incident reflectivity at 120 nm incident wavelength was obtained, which corresponded to the optimum thickness of Ir layer of 12 nm. Ir layer of too thin or thick thickness cannot get high reflectivity. The annealing of the layer benefits the release of tension, but it also causes the increase of average size of Ir grain and degradation of the reflectivity.