In　order　to　investigate　the　influences　of　temperature　gradient　on　space　charge　and　electric　field　distribution　under　different　operating　conditions　of　XLPE　insulated　HVDC　cable,　we　review　and　summarize　the　current　technical　test　standards　and　evaluation　methods　of　HVDC　cable,　and　present　the　system　development　for　HVDC　cable　long-term　performance　assessment　and　space　charge　measurement　under　operation　condition　with　temperature　difference　through　the　insulation　thickness.　The　long-term　performance　evaluation　test　and　space　charge　measurement　of　a　HVDC　cable　and　accessories　under　different　operating　conditions　are　carried　out　by　using　this　test　system,　and　the　results　are　briefly　discussed.　The　system　has　the　ability　to　achieve　the　maximum　test　temperature　difference　within　the　insulation　layer　up　to　40℃　and　space　charge　measurement　on　full　size　cable　with　insulation　thickness　as　high　as　16　mm.　The　accumulation　of　hetero-charge　near　the　outer　semi-conductive　layer　having　lower　temperature　is　obvious　under　controlled　temperature　gradient,　and　the　charge　density　increases　greatly　with　temperature　difference　increasing.　The　interfacial　electric　field　is　unacceptably　distorted　due　to　this　space　charge　accumulation,　and　the　electric　field　strength　at　this　interface　is　almost　twice　the　average　field　strength　under　uniform　temperature　when　the　temperature　difference　reaches　40℃.　©　2018,　High　Voltage　Engineering　Editorial　Department　of　CEPRI.　All　right　reserved.