With　the　aging　of　the　oil-paper　insulation　system,　the　polarization　responses　would　be　more　complex　owing　to　a　large　number　of　aging　products.　In　this　case,　the　well　known　extended　Debye　model　cannot　reflect　the　relaxation　process　of　the　oil-paper　insulation　system　actually.　Therefore,　a　mixed　polarization　circuit　model　based　on　the　equivalent　circuit　model　and　the　extended　Debye　model　is　put　forward.　The　proposed　model　can　reflect　the　relaxation　process　of　the　oil-paper　insulation　system　more　actually.　Secondly,　the　method　for　parameter　identification　is　given,　and　the　alignment　method　is　adopted　to　confirm　the　branch　number　of　the　equivalent　circuit.　Finally,　the　results　of　example　analysis　and　comparison　confirm　that　the　mixed　polarization　circuit　model　has　higher　accuracy　than　that　of　the　ED　equivalent　circuit　model,　and　the　relaxation　process　of　the　insulation　system　is　closer　to　the　actual　one.　©　2016,　The　editorial　office　of　Transaction　of　China　Electrotechnical　Society.　All　right　reserved.