Enhancing　the　thermal　conductivity　of　insulation　materials　can　reduce　the　operating　temperature　and　thus　increase　the　transmission　capacity　of　power　cables.　In　this　work,　low　density　polyethylene　(LDPE)　with　the　fillers　of　magnesium　hydroxide　(Mg(OH))　was　selected　as　the　base　insulation　materials　for　fire　retardant.　Boron　nitride　nanosheets　(BNNs)　were　selected　as　the　fillers　to　increase　the　thermal　conductivity.　To　imitate　the　melt　extrusion　in　cable　manufacturing　process,　composites　with　different　filler　ratios　were　prepared　by　HAAKE　Polylab　OS　and　then　molded　at　high　pressure.　The　thermal　conductivities　of　the　composites　were　measured　by　LFA447　nanoflash　and　the　microstructures　of　composites　were　observed　by　the　scanning　electron　microscope　(SEM).　The　filler　orientation　was　characterized　by　diffraction　of　X-rays　(XRD)　to　represent　the　anisotropic　index　of　the　composites.　The　results　indicated　that　BNNs　were　inclined　to　be　oriented　along　the　extrusion　plane　because　of　the　axial　pressure　in　molding　process.　As　a　result,　the　composites　showed　anisotropic　thermal　conductivity.　For　example,　in　the　composites　with　20wt%　BNNs,　the　thermal　conductivity　in　through-plane　direction　reached　3.97W/(m·K),　which　was　1240%　of　that　of　LDPE.　Furthermore,　with　the　addition　of　Mg(OH),　the　thermal　conductivity　of　the　composite　was　further　improved,　and　the　thinner　flake　samples　showed　stronger　anisotropy　in　thermal　property.　It　was　shown　that　the　multi-packing　structure　molded　by　the　simple　melt-blending　process　was　a　feasible　method　to　fabricate　high　efficiency　thermally　conductive　composites.　©　2021　IEEE.