Based　on　the　hybrid　equivalent　model　of　oil-paper　insulation　(HEM),　the　interface　polarization　branch　is　introduced　into　the　topology　of　the　extended　Debye　model　(EDM),　and　new　frequency　domain　characteristic　parameters　PTC-Max　and　PTC-Min　that　characterize　the　moisture　content　of　oil-impregnated　paper　are　extracted.　Firstly,　according　to　the　measured　induction　voltage　regulator　data,　the　difference　of　FDS　in　identifying　the　parameters　of　HEM　and　EDM　models　is　compared　to　explain　the　advantages　of　HEM.　The　transfer　function　equation　of　the　model　is　derived　by　the　transfer　function　method,　and　the　transfer　function　spectrum　of　oil-impregnated　paper　with　different　moisture　content　is　obtained　through　Matlab　analysis.　Then,　the　HEM　polarization　branch　pole　can　be　used　to　characterize　the　moisture　content　of　oil-impregnated　paper.　The　linear　combination　of　evaluation　equations　corresponding　to　the　two　characteristic　parameters　is　realized　by　the　optimal　weighted　combination　method,　which　overcomes　the　shortcomings　of　the　single　evaluation　equation.　Finally,　by　the　measured　data　of　different　sizes　of　oil-paper　insulation　equipment,　the　validity　of　the　extracted　characteristic　parameters　is　tested.　©　2021,　Electrical　Technology　Press　Co.　Ltd.　All　right　reserved.