Blue light emitting glass and the preparation method thereof are provided. The blue light emitting glass has the following composition: aCaO.bAl2O3.cSiO2.xCeO2, wherein a, b, c and x are, by mol part, 15-55, 15-35, 20-60 and 0.01-5 respectively. The preparation method comprises: weighing the raw materials according to the composition of the blue light emitting glass; mixing the raw materials uniformly and melting the raw materials to obtain glass melt; moulding the glass melt to obtain transparent glass; thermally treating the transparent glass under reducing atmosphere, and thereafter obtaining the finished product. The blue light emitting glass obtained has intense broadband excitation spectrum in ultraviolet region and emits intense blue light under the excitation of ultraviolet light. It is suitable for using as luminescent medium material.