Polyimide composites have attracted more and more attention due to their excellent properties and wide application prospects in aerospace, rail transit, microelectronics and other fields. SiC@SiO₂ whisker was prepared by oxidation of SiC whisker at 750 ℃, which formed mixed fillers with BN particles. The SiC@SiO₂ whisker and BN were modified by a silane coupling agent and a titanate coupling agent, respectively. SiC@SiO₂/BN/PI composites were prepared by in-situ polymerization. The structure and property of the fillers and composites were characterized. Whiskers and particles formed an effective pathway in the polyimide matrix, which promoted continuous improvement of the thermal conductivity of SiC@SiO₂/BN/PI composites. When the total filler content was 45wt% and the mass ratio of whiskers to particles was 4 : 1, the thermal conductivity was increased to 0.95 W/(m·K). Mechanical properties of SiC@SiO₂/BN/PI composites changed regularly with the type and amount of mixed fillers. The SiO₂ layer blocks the communication of free electrons between the mixed fillers, and the decreasing range of electrical insulation performance of the SiC@SiO₂/BN/PI composites declined.