In　order　to　study　the　influence　of　temperature　gradient　on　long-term　reliability　of　high　voltage　direct　current　(HVDC)　cross-linked　polyethylene　(XLPE)　cable　insulation　during　actual　operation,　homemade　temperature　gradient-DC　field　cooperative　aging　device　for　multi-group　sheet　specimen　were　used　to　carry　out　temperature　gradient-DC　stress　cooperative　aging　on　three　kinds　of　XLPE　insulating　materials　(including　domestic　XLPE,　nano-modified　XLPE　and　HVDC　XLPE　produced　by　Borealis).　Furthermore,　traditional　thermo-electrical　aging　were　performed　on　above　three　kinds　of　XLPE　as　parallel　group.　Space　charge　characteristics　of　the　three　kinds　of　XLPE　after　aging　for　different　times　(one　month　and　three　months,　respectively)　were　measured　by　pulsed　electro-acoustic　(PEA)　method.　Moreover,　resistivity　and　infrared　spectrum　of　the　XLPE　before　and　after　aging　were　measured,　respectively.　Results　show　that　the　space　charge　distribution　evenly　in　the　bulk　of　thermo-electrically　aged　specimens,　while　hetero-charge　in　the　specimens　aged　under　temperature　gradient　mainly　accumulate　near　electrodes,　and　resistivity　of　the　XLPE　decrease　with　aging　time.　Furthermore,　the　resistivity　of　thermo-electrical　aged　samples　are　lower　than　those　that　aged　under　temperature　gradient　at　the　same　time.　In　addition,　domestic　nano-modified　XLPE　has　the　smallest　carbonyl　absorption　peak　value,　which　indicates　the　lowest　aging　degree　and　the　least　space　charge　accumulation　in　the　samples.　©　2016　Chin.　Soc.　for　Elec.　Eng.