In this study, nanocrystalline La1-xEuxB6 powders were successfully fabricated using a novel calcium thermal reduction and acid leaching technique (CTR&AL) for the first time, and the effect of Eu-doping on the structure and optical properties of La1-xEuxB6 and the mechanism were also systematically investigated. The XRD, FE-SEM and TEM analyses all confirm that the nanocrystalline La1-xEuxB6 exhibits a single-phase CsCl-type cubic structure, good crystallinity and a cubic morphological characterization with an average grain size of 40 nm. The results of optical absorption show that the transmission light wavelength of nanocrystalline La1-xEuxB6 shifts from 595 nm to 825 nm with increasing Eu-doping content, indicating a "red shift" phenomenon of transmission light. And the Eu doping causes the enhancement and broadening of absorption spectrum of LaB6 in the near-infrared region. Furthermore, the first principle calculations reveal that the Eu-doping strengthens the localization of energy bands at near Fermi level of LaB6 and reduces the number of conduction electrons in the conduction band, which in turn decreases its plasmon resonance frequency energy, which qualitatively explains the continuous tunable characteristic of La1-xEuxB6 transmission light.