In　order　to　understand　the　difference　of　dielectric　properties　and　their　mechanisms　between　AC　and　DC　high　voltage　XLPE　cables　used　insulation　materials,　Fourier　transform　infrared　spectra　(FTIR),　X-ray　diffraction　(XRD),　DC　electrical　conductivity　and　thermal　stimulated　currents　were　measured　to　compare　the　dielectric　properties　and　analysis　the　contact　between　DC　electrical　conductivity　and　trap　characteristics.　The　results　showed　that　the　DC　cable　used　XLPE　(DC-XLPE)　had　a　relative　high　DC　conductivity　than　that　of　the　AC　cable　used　XLPE　(AC-XLPE)　at　the　test　temperatures　and　this　was　governed　by　the　shallow　trap　densities.　The　activation　energies　of　the　conductivity　were　0.89　eV　and　1.09　eV　for　DC-XLPE　and　AC-XLPE　respectively　and　this　were　same　with　the　energy　depths　of　the　bulk　deep　traps.　The　results　of　the　FTIR　proved　that　the　higher　energy　depth　of　the　bulk　deep　traps　of　AC-XLPE　was　caused　by　its　higher　content　of　polar　groups　such　as　carbanyl　groups.　The　crystallinities　of　the　samples　measured　by　XRD　had　no　obvious　difference　and　they　were　49%　and　50%　for　DC-XLPE　and　AC-XLPE　respectively.　As　a　result,　it　should　be　paid　attention　to　reduce　the　content　of　polar　groups　in　the　design　of　HVDC　used　XLPE　to　get　a　better　DC　insulation　properties.