With the increase of packaging density of power electronic devices, the development of thermal interface materials with excellent thermal conductivity has received widely spread attention. Due to most traditional heat conductors showing relatively low thermal conductivity, synthesis of new high thermal conductive fillers is an important way to improve the thermal conductivity of thermal interface materials. In this study, boron phosphide (BP) particles were synthesized by a facile molten salt method, then mixed with boron nitride (h-BN) and filled into epoxy resin (EP) to prepare epoxy resin matrix composites (BP-BN/EP) by stirring and casting. With the three salts (NaCl : KCl : LiCl) method, the experimental data showed that the highest yield of BP reached 74%, 33% and 35% higher than that of the single salt method (41%) and the double salt method (39%), respectively. In the BP-BN/EP composites, BP and BN particles were uniformly dispersed in the EP matrix. When the hybrid filler loading at 30% (in volume), the thermal conductivity reached 1.81 W·m^-1·K^-1, 8.6 times of that of pure epoxy (0.21 W·m^-1·K^-1). The thermal conductivity improvement was related to the construction of thermal conductive network by BP particles linking adjacent BN sheets. In addition, to excellent thermal conductivity, the BP-BN/EP composites also showed good thermal stability and good thermodynamic properties. Therefore, the synthesized BP by molten salt method has great application prospects in the field of heat management.