Abstract: The BN fiber-graphene nanoplatelets/polypropylene (BN fiber-GNP/PP) high thermal conductivity electrical insulation composite was prepared by melt blending. The effects of BN fiber content and length on the thermal insulation properties of BN fiber-GNP/PP composites were investigated by finite element simulation, SEM, XRD and thermal conductivity test results. The results show that the increase of BN fiber content and length in BN fiber-GNP/PP composites can increase the range of GNP distribution and the contact probability of BN fiber with GNP. At 7wt% GNP content, the addition of 100 μm BN fiber at 20wt% makes the thermal conductivity of BN fiber-GNP/PP composites 4.2 times higher than PP, while the electrical insulation is slightly improved. The simulation results show that the addition of high content of 100 μm BN fiber tends to complete the thermal network of BN fiber-GNP/PP composites and reduce the area of local heat flux. Under the influence of the "synergistic effect" of flake GNP and fibrous BN two-phase filler, GNP and BN fibers form a special "dual network" structure as "islands" and "bridges", respectively. The BN fiber acts as a high thermal conductivity "bridge" to block the formation of conductive pathways between adjacent GNP. The thermal insulation properties of the BN fiber-GNP/PP composite are improved.