In this article, thermal evaporation technology was employed to deposit erbium fluoride films on germanium(111) substrates. XRD diffraction pattern shows that films turn from amorphous to crystalline with the increase of substrate temperature. Correspondingly, the morphology and infrared optical properties change obviously. The infrared transmission spectrum of the partially crystalline film is homologous to the totally amorphous film but not the crystalline films. Crystal lattice parameters calculation indicates that there is great compression thermal stress in the erbium fluoride film deposited at high deposition temperature. The refractive indices and extinction coefficients of the films were calculated by fitting the infrared transmission spectrum using Lorentz oscillator model. The refractive index and extinction coefficients at 10μm for the amorphous erbium fluoride film are n=1.38 and k=0.01, and for crystalline films are n=1.32 and k=0.006, respectively.