A series of samples of hexagonal boron nitride-aluminum nitride ceramic composites with different amounts of CaF2 as sintering aid were prepared by spark plasma sintered at 1700–1850 °C for 5 min. The addition of CaF2 effectively lowered the sintering temperature and promoted the densification of AlN-BN composites. With the increase of sintering temperature, the density increased, and the contiguity of AlN grains enhanced in AlN-BN composites. Thermal conductivity of AlN-BN composites increased with the increase in CaF2 content and sintering temperature, and there is a maximum value of 78.6 W·m−1·K−1 when the sample with 3wt% CaF2 sintered at 1800 °C.