This　paper　investigates　the　aging　properties　of　oil-paper　insulation　under　thermocorona　discharge.　The　oil-paper　insulation　samples　were　heated　and　kept　at　140°C,　and　a　corona　discharge　was　generated　with　a　needle-plate　at　a　frequency　of　15　times/day,　with　each　discharge　lasting　5　minutes.　The　aging　properties　of　oil-paper　insulation　were　investigated　by　measuring　the　degree　of　polymerization　(DP)　of　insulation　paper　samples　along　with　the　furfural　content　and　acid　value　of　the　transformer　oil　samples.　The　results　show　that　corona　discharge　at　140°C　in　oil　rapidly　decreased　the　insulation　paper　DP　and　increased　the　furfural　content　and　acid　value　of　the　oil　compared　with　thermal　aging　and　corona　discharge　aging　at　20°C.　The　DP　of　the　insulation　paper　was　reduced　to　392.12,　the　furfural　content　in　oil　rose　to　33.75　mg/L,　and　the　acid　value　grew　to　4.41　mgKOH/g　after　15　days　under　the　combined　thermal　stress　and　corona　discharge.　Both　electric　and　thermal　stress　accelerated　the　aging　of　oil-paper　insulation.　This　research　has　practical　significance　for　understanding　the　process　of　insulation　failure　caused　by　the　accelerated　aging　of　oil-paper　insulation.　©　2019　IEEE.