CBS/Al2O3 glass ceramic composites green tapes were prepared by using CaO-B2O3-SiO2 (CBS) glass, Al2O3 powders and Li2CO3 powders. Results showed that Li2CO3 could react with CBS and Al2O3 to form Li4B2O5 and LiAlO2 in low melting phase, which would promote sintering process of CBS/Al2O3 composites and reduced the sintering temperature to 850 ℃ with a density of 2.63 g/cm3 and a dielectric constant of 7.24, dielectric loss of 1.57×10-3. The exceptional thermal conductivity could be attained 15.16 W/(m·K), when the hole share and width was 3.88% and 1.00 mm by co firing with high thermal conductivity silver, which outweighed that of AlN/glass substrate.