The　microstructure　of　a　fully　activated　scandia　doped　dispenser　(SDD)　cathode　has　been　studied　by　scanning　electron　microscope　(SEM).　The　observation　results　display　that　nanoparticles　appear　at　the　growth　steps　and　the　surface　of　tungsten　grains　of　the　fully　activated　SDD　cathode.　To　study　the　influence　of　the　nanoparticles　on　the　emission,　the　local　electric　field　strengths　around　the　nanoparticles　have　been　calculated　by　Maxwell　2D　code　and　Comsol.　The　calculation　results　show　that　the　local　electric　field　strengths　are　enhanced　by　1.1　to　3.8　times　to　average　value　based　on　different　model　conditions.　The　highest　field　strength　is　about　1.54　x　10(5)　V/cm　at　an　average　field　strength　of　40　KV/cm,　which　is　related　to　a　space-charge　limited　(SCL)　current　density　of　100　A/cm(2)　in　the　experimental　configuration.　This　implies　the　field　strength　is　not　high　enough　to　cause　field　emission.