The mixed SrF2-CaF2 thin films with the same thickness were deposited by the techniques of resistant evaporation and electron beam evaporation respectively. The physical and infrared optical properties of the thin films were investigated. The optical constants in the infrared region were determined quantitatively which fills the gap of these data. At the same time, we provided a method to obtain gradient index films. We also used the mixed SrF2-CaF2 with a proportion of 1∶1 as the lower index material to deposit multilayer coatings. A broadband antireflection coatings with high optical performance was developed.