Medium　voltage　cables　are　widely　used　in　various　distribution　networks.　The　cable　joint　are　prone　to　discharge　defects　during　installation　and　operation　to　destroy　their　insulation　structure.　In　order　to　study　the　impact　of　different　defects　on　the　electric　field　strength　of　the　cable　joint,　this　paper　established　a　26/35 kV　XLPE　in　SolidWorks.　The　three-dimensional　physical　model　of　the　cable　body　and　the　cable　joint　is　designed　with　four　typical　defects　models　of　air　gap,　cut,　impurity　and　scratch.　These　typical　defects　was　simulated　by　finite　element　method　(FEM)　in　the　three-dimensional　electric　field　simulation　of　CST　STUDIO　and　through　comparison　to　get　the　influence　of　defects　on　the　electric　field　strength.　The　results　show　that　these　four　kinds　of　defects　will　increase　the　electric　field　strength　of　the　cable　joint　and　even　lead　to　a　huge　failure　caused　by　insulation　breakdown.　It　provides　an　important　reference　for　diagnosis　of　the　insulation　condition　monitoring　of　the　cable　joint　in　the　future.　Ensure　the　safety　and　reliability　of　power　system　operation.　©　2021,　Beijing　Oriental　Sun　Cult.　Comm.　CO　Ltd.