The crystallization and optical spectra of the Cr 3+ doped K 2O-ZnO-Al 2O 3-B 2O 3-SiO 2 glasses were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), absorption spectra and fluorescence spectra. The experimental results show that the addition of ZnO to the Cr 3+ doped K 2O-Al 2O 3-B 2O 3-SiO 2 glass makes the crystallizability of glass improve obviously, the crystalline temperature decrease and the nanometre grade mullite micro-crystal more uniform and regular. As a result the luminescence of glass-ceramics is stronger.