A　novel　electrode　structure　consisting　of　a　variable　spacing　interdigital　electrode　(VS-IDE)　was　proposed　for　assessing　of　the　aging　of　silicone　rubber　sheds　with　variable　thickness.　A　series　of　numerical　simulations　and　experiments　have　been　carried　out　to　investigate　the　influences　of　finger　number,　unit　width,　and　metallization　ratio　on　the　signal　strength　and　penetration　depth　of　sensors　with　a　traditional　inter　digital　electrode　structure.　According　to　the　relationship　between　the　penetration　depth　and　the　unit　width,　the　width　of　each　finger　that　composed　the　VS-IDE　structure　sensor　was　optimized　individually　to　confine　the　electric　field　line　within　the　sheds　under　test.　Experimental　results　showed　that　compared　to　the　other　sensors,　the　optimal　sensor　exhibited　high　amplitude,　high　sensitivity,　and　excellent　stability　against　the　effects　of　environmental　humidity.　The　developed　capacitive　proximity　sensors　have　been　used　for　assessing　of　the　aging　of　silicone　rubber　sheds　in　composite　insulators,　and　the　feasibility　of　assessing　insulation　degradation　by　quantitative　capacitive　techniques　is　demonstrated.　(C)　2016　Elsevier　B.V.　All　rights　reserved.