Aiming　at　the　problem　of　aging　of　composite　insulator,　a　composite　insulator　with　seven　years　running　history　at　power　grid　is　analyzed.　Its　electric　field　is　computed　through　finite　elements　method,　and　the　electric　field　intensities　at　different　umbrellas　are　compared.　The　microstructures　of　silastic　aged　under　electric　and　ultraviolet　effects　are　also　compared　by　analyzing　the　SEM　photos　of　different　silastic　sections　of　the　umbrellas.　The　comparison　between　the　microstructures　of　top　and　bottom　surfaces　of　umbrella　demonstrates　the　rules　of　electric　aging　and　electric　erosion.　The　possibility　of　surface　contamination　moving　inside　silastic　is　studied　via　energy　spectrum　analysis.　The　results　will　be　helpful　for　research　of　composite　insulator　aging　and　optimization　design　of　anti-aging.