The paper aims to discuss and compare the effects of nitride ceramic particles AlN and BN on the thermal conductivity of thermoplastic phenolic resin composites, prepare high-thermal composite materials and apply them to electronic plastic packaging. Firstly, AlN and BN were surface-modified with a silane coupling agent to enhance the dis-persibility in the organic polymer. Then, by adding the ceramic particles different size to the linear phenolic resin, the effects of particle of sizes, the effects of particle size and filler content on the thermal conductivity of the linear phenolic resin composite were compared to obtain filler for improving the thermal conductivity of the composite from the phonon point of view. The experimental results showed that after surface modification, the contact angles of the ceramic particles AlN and BN with water became large; while those angles with resin became small. So the silane coupling agent made the filler dispersed better in the novolac resin than in water. AlN and BN with different particle sizes were filled with linear phenolic resin at different contents. The effect of filler particle size on the thermal conductivity of the composite was different with different contents. According to the heat transfer analysis of phonon, BN transferred heat easier than AlN at the interface formed with C, achieving high thermal conductivity. Nitride ceramic particles can well enhance the thermal conductivity of the composite, especially BN. The overlap of density of states (DOS) of BN and C are extremely high, which is more suitable for rapid heat transferring at BN and C interfaces.