Different　degrees　of　electrical　aging　test　for　PPLP　insulation　is　carried　out　to　study　the　aging　mechanisms　of　polypropylene　laminated　paper　(PPLP),　which　is　the　major　insulation　of　high　temperature　superconducting　(HTS)　cables.　Effects　of　electrical　aging　on　the　breakdown　performance　and　trap　distribution　of　PPLP　insulation　are　studied　by　AC　breakdown　and　isothermal　surface　potential　decay　(ISPD)　measurements.　And　the　aged　samples　are　further　analyzed　by　Fourier　transform　infrared　spectrum,　morphology　observation　and　thermogravimetric　analysis.　Results　show　that　with　the　increase　of　electrical　agingdegree,　AC　breakdown　field　strength　of　PPLP　insulation　decreases　from　113.3　kV/mm　to　92.3　kV/mm.　The　density　of　shallow　traps　increases　gradually　while　that　of　deep　traps　decreases　gradually　during　aging　process.　It　is　observed　that　the　partial　cellulose　in　the　insulating　paper　of　the　PPLP　out　layer　is　broken,　and　a　great　number　of　voids　are　generated,　resulting　in　loose　structure　and　reduced　strength.　The　IR　absorption　peak　intensities　of　hydrogen　bond　and　glycoside　bond　in　the　insulating　paper　decrease.　Meanwhile,　the　temperature　of　fastest　thermal　weight　loss　of　insulating　paper　decreases,　while　the　thermal　weight　loss　of　polypropylene　keeps　stable.　The　experimental　results　reveal　that　the　degradation　of　PPLP　insulation　performances　during　aging　is　mainly　attributed　to　the　deterioration　of　insulating　paper.　The　analysis　shows　that　the　glycoside　bonds　in　the　main　chain　of　cellulose　and　the　hydrogen　bonds　between　cellulose　molecules　break　under　the　impact　of　high　energy　electrons.　As　a　result,　the　interaction　force　among　molecular　chains　weakens　and　the　structural　compactness　decreases.　The　internal　free　volume　of　insulating　paper　increases,　and　the　binding　ability　of　cellulose　molecular　chains　to　charges　weakens,　so　the　electric　charges　migrate　more　easily　between　molecular　chains,　resulting　in　the　decrease　of　deep　trap　density　and　AC　breakdown　field　strength　of　PPLP　insulation.　©　2020,　Editorial　Office　of　Journal　of　Xi＇an　Jiaotong　University.　All　right　reserved.