This　paper　utilizes　a　hybrid　Debye　model　to　accurately　simulate　the　relaxation　response　process　of　the　oil-paper　insulation　of　a　transformer　to　explore　the　application　of　frequency　domain　dielectric　spectroscopy　(FDS)　in　nondestructive　diagnosis　of　the　aging　condition　of　oil-paper　insulation.　Via　FDS　test　data,　the　model　parameters　can　be　identified,　and　the　influence　laws　of　FDS　can　be　obtained　through　the　variation　of　model　parameters.　To　explore　the　effects　of　insulating　paper　moisture　content,　insulating　paper　layers,　and　test　temperature　on　FDS　characteristics,　an　FDS　experimental　platform　is　established.　The　results　show　that　the　hybrid　Debye　model　can　effectively　reflect　the　relaxation　response　process　of　oil-paper　insulation　under　different　conditions,　as　well　as　that　a　physical　relationship　between　the　model　parameters　and　oil-paper　dielectric　polarization　exists.　In　addition,　the　parameters　of　the　hybrid　Debye　model　can　be　used　as　the　characteristic　quantities　for　the　non-destructive　evaluation　of　the　oil-paper　insulation　state,　providing　new　ideas　for　the　non-destructive　evaluation　of　the　oil-paper　insulation　state.　©　2021　The　Authors.　IET　Science,　Measurement　&　Technology　published　by　John　Wiley　&　Sons　Ltd　on　behalf　of　The　Institution　of　Engineering　and　Technology