Pre-crosslinking　is　likely　to　occur　during　the　extrusion　process　of　cross-linked　polyethylene　(XLPE)　used　for　high　voltage　cables,　which　has　negative　effects　on　the　extrusion　molding　of　XLPE　insulation.　Adding　antioxidants　contributes　to　delaying　the　pre-crosslinking,　so　different　insulating　materials　with　three　kinds　of　isomers　of　hindered　phenolic　antioxidants　are　investigated,　respectively.　The　experimental　results　show　that　the　insulating　materials　added　with　antioxidant　736　has　a　better　effect　on　delaying　pre-crosslinking,　but　its　final　cross-linking　degree　is　lower.　Bond　dissociation　energy　(BDE)　and　energy　band　distribution　of　different　antioxidant　molecules　were　obtained　by　first-principles　calculation.　Besides,　AO736　has　lower　BDE　compared　with　AO2246-S　and　AO300,　which　reflects　better　free　radical　eliminating　and　delaying　pre-crosslinking　abilities.　What　is　more,　AO736　can　produces　deep　hole　traps,　which　enhances　the　ability　to　capture　carriers,　thereby　reducing　its　average　free　path　and　weakening　the　damage　of　collision　ionization　to　molecular　chains.　So　it　can　significantly　improve　DC　breakdown　strength　of　XLPE.　This　study　shows　that　AO736　has　potential　application　prospect　in　XLPE　insulating　materials.　©　2022　IEEE.