Resin-impregnated　paper　(RIP)　bushings　have　been　widely　used　in　power　system,　however　failure　caused　by　local　inter-foil　insulation　deterioration　has　occurred　from　time　to　time,　which　has　seriously　affected　the　safe　and　stable　operation　of　substations.　Due　to　the　damaging　effect　of　partial　discharge,　the　resistance　of　local　inter-foil　insulation　will　gradually　decrease,　and　breakdown　may　even　occur.　To　study　the　phenomenon　of　local　inter-foil　insulation　deterioration　of　RIP　bushing,　a　test　platform　is　established　for　72.5kV　RIP　transformer　bushings,　and　corresponding　frequency-domain　dielectric　spectroscopy(FDS)　test　is　conducted　at　room　temperature.　It　is　found　that　the　FDS　curve　of　bushing　with　inter-foil　insulation　deterioration　and　breakdown　is　significantly　shifted　compared　to　the　normal　one.　In　addition,　due　to　the　obvious　development　process　of　local　inter-foil　insulation　deterioration　of　RIP　bushings,　a　simulation　model　is　established　in　this　paper,　and　the　method　of　changing　the　local　electrical　conductivity　of　local　inter-foil　insulation　material　is　used　to　characterize　the　degree　of　insulation　deterioration,　and　corresponding　FDS　response　curves　are　obtained.　The　results　show　that　with　the　development　of　the　deterioration　of　local　inter-foil　insulation,　the　C-f　and　tant5-f　curves　have　obvious　transitional　processes.　In　the　initial　and　middle　stage　of　insulation　deterioration,　the　FDS　method　has　higher　diagnostic　effectiveness　than　the　traditional　power　frequency　dielectric　loss　method.　This　article　can　provide　a　basic　theoretical　reference　for　the　on-site　diagnosis　of　local　inter-foil　insulation　deterioration　of　RIP　bushings.　©　2018　IEEE.