The invention provides a preparation method of a BN / epoxy resin heat conductive insulation composite material and belongs to the field of preparation of heat conductive insulation composite materials.The method includes: firstly, performing annealing pretreatment to BN powder and then surface modification with a silane coupling agent; then according to certain ratio, filling an epoxy resin matrixwith the modified hexagonal BN micropowder and the modified cubic BN micropowder. The method is simple process, wherein by adding the BN in different appearances, dimensions and phase structures, effective heat conduction channels are formed to finally improve the heat conductivity of the epoxy resin. After modification, the interface combination between the HBN and the resin is strong, wherein the sheet-like HBN and bulk CBN are overlapped in the epoxy resin to form excellent heat conductive network, thus effectively reducing interfacial thermo-resistance. The composite material is beneficial to quick transmission of heat, improves heat conductivity of the epoxy resin, has excellent insulation performance, and is improved in mechanical property.