Mixed-valence Eu-doped transparent oxyfluoride glass-ceramics containing cubic LaF3 nanocrystals were fabricated by traditional melt-quenching technique and consequent annealing processes. Their structural and luminescent properties were systemically investigated by X-ray diffraction (XRD), transmission electron microscopy, absorption, excitation, emission spectra, and fluorescence lifetime measurements. Analyses of XRD patterns prove that the new precipitated nanocrystals disperse in glass-ceramics crystallize in cubic LaF3. The spectroscopic investigations show that Eu2+ ions have been incorporated into the LaF3 nanocrystals preferentially, while Eu3+ ions still remain in the glass phase after crystallization. Based on the spectral results, a new parameter Rchange=RGC-RPG/RGC was defined to describe the changes of the environments of Eu3+ before and after crystallization more straightforwardly and more sensitively, where R-PG and R-GC represent the integrated intensity radio of D-5(0) -> F-7(2) to D-5(0) -> F-7(1) emissions of Eu3+ in PG and GC samples, respectively. Our investigation will not only enrich the understanding of fluoride nanocrystals-based oxyfluoride glass-ceramics, but also the distribution and luminescence behaviors of Eu3+ ions in them.