The effects of depositing temperature on structure and optical properties of resistant-boat evaporated LaF3 single layers were investigated. The films were produced at different temperatures from 200℃ to 350℃ by increasing step of 50℃. The optical loss, optical constants, optical band gap and cut-off wavelength were deduced on the basis of the transmittance and reflectance curves. Profile and surface roughness measurement instrument was used to determine the rms surface roughness. Microstructure of the samples was characterized by X-ray diffraction (XRD). It was found that the total optical loss，the grain size and the rms surface roughness increased with the increasing of the depositing temperature at the short wavelength period. And the increasing total optical loss with depositing temperature was attributed to the absorption because the scattering occupied the very low percent in the whole loss. The samples deposited at higher temperature had the higher refractive index and extinction coefficient and lower optical band gap. The cut-off wavelength shifted to the long wavelength as the depositing temperature increased.