In　this　paper,　in　order　to　study　the　effect　of　temperature　gradient　on　long-term　reliability　of　high　voltage　direct　current　(HVDC)　cross-linked　polyethylene　(XLPE)　cable　insulation　during　actual　operation,　an　aging　device　under　DC　electrical　stress　companied　with　temperature　gradient(　the　high　temperature　side　is　60　degrees　C　and　the　low　temperature　side　is　20　degrees　C)　for　multi-group　film　specimen　were　designed　to　carry　on　three　kinds　of　XLPE　insulating　materials,　which　includes　pure　XLPE,　nano-modified　XLPE　and　HVDC　XLPE　produced　by　Borealis).　Furthermore,　traditional　thermo-electrical　aging　at　a　constant　temperature　of　60　degrees　C　were　performed　on　above　three　kinds　of　XLPE　as　reference　group.　Space　charge　characteristics　of　the　three　kinds　of　XLPE　after　aging　for　different　months　were　measured　by　pulsed　electro-acoustic　(PEA)　method.　Moreover,　resistivities　of　the　three　kinds　of　XLPE　after　aging　were　measured,　respectively.　Results　show　that　space　charge　distributes　evenly　in　the　specimens　with　a　constant　temperature,　while　hetero-charge　accumulates　in　the　specimens　under　temperature　gradient.　Moreover,　resistivities　of　the　three　kinds　of　XLPE　decrease　with　the　increasing　aging　time.　Furthermore,　the　resistivities　of　aged　samples　under　temperatrue　gradient　were　lower　than　those　of　thermo-electrical　aged　samples　at　the　same　time.　Compared　with　the　other　samples,　the　space　charge　accumulation　in　2#　XLPE　samples　was　least　in　the　same　operation　condition,　which　shows　2#　samples　were　aged　at　lowest　degree.