Silicone　rubber　(SR)　is　extensively　used　as　insulation　for　cable　accessories,　directly　affecting　their　design　and　operation.　The　distinctive　feature　of　cable　accessory　insulation,　operating　under　mechanical　stretching,　has　not　received　sufficient　attention　in　relevant　standards　and　research.　This　study　investigates　two　essential　electrical　parameters　of　SR　insulation:　relative　permittivity　and　AC　breakdown　strength,　analysing　and　summarising　their　variations　during　mechanical　stretching.　By　comparing　the　parameter　variations　of　SR　samples　with　different　filler　contents　and　matrix　compositions,　the　microscopic　stretching　behaviour　and　performance　change　mechanisms　under　mechanical　stretching　are　explored.　The　results　reveal　the　tensile　effect　on　SR　insulation,　demonstrating　that　as　the　stretching　ratio　increases,　the　relative　permittivity　decreases,　whereas　the　AC　breakdown　strength　shows　an　increasing　trend.　Increasing　filler　content　and　incorporating　low　molecular　weight　components　suppress　the　tensile　effect,　whereas　decreasing　filler　content　has　the　opposite　effect.　Given　the　significant　correlation　between　these　two　parameters,　the　orientation　and　elongation　of　molecular　chains　are　considered　the　primary　factors　influencing　the　tensile　effect　on　SR　insulation.　This　insight　proposes　a　novel　approach　to　control　and　optimise　the　performance　of　cable　accessory　insulation.　©　2025　The　Author(s).　High　Voltage　published　by　John　Wiley　&　Sons　Ltd　on　behalf　of　The　Institution　of　Engineering　and　Technology　and　China　Electric　Power　Research　Institute.