The　furfural　content　in　transformer　oil　only　comes　from　the　aging　of　the　insulating　paper　in　oil-paper　insulation　transformer,　which　has　important　guiding　significance　for　the　aging　diagnosis　of　transformer　solid　insulation.　This　paper　firstly　analyzes　the　relationship　between　the　equivalent　circuit　parameters　and　the　insulation　aging　of　the　transformer　theoretically,　uses　the　improved　particle　swarm　algorithm　to　effectively　identify　the　equivalent　circuit　parameters　of　three　transformers　with　different　aging　conditions,　and　finally　analyzes　the　relationship　between　the　furfural　content　in　the　transformer　oil　and　the　relaxation　response　equivalent　circuit　parameters　of　the　transformer　insulation　system.　The　research　results　show　that　the　change　of　furfural　content　in　transformer　oil　has　the　largest　effect　on　the　large　time　constant　branch　circuit　parameters　of　the　equivalent　circuit;　the　more　serious　the　transformer　insulation　aging　is,　the　higher　the　furfural　content　in　the　oil　becomes,　the　smaller　the　time　constant　of　the　large　time　constant　branch　circuit　becomes,　the　smaller　the　polarization　resistance　becomes,　and　the　larger　the　polarization　capacitance　becomes;　and　the　furfural　content　has　good　function　relationship　with　the　time　constant　of　the　large　time　constant　branch　circuit,　which　provides　a　new　method　to　quantitatively　determine　the　furfural　content　in　transformer　oil.　When　the　time　constant　of　the　large　time　constant　branch　circuit　reaches　to　134.07s,　the　insulation　aging　of　the　transformer　is　serious.　©　2016,　Science　Press.　All　right　reserved.