Insertion　loss　(IL)　of　EMI　filter　is　closely　related　to　noise　source　impedance　and　load　impedance.　Therefore,　in　order　to　make　the　EMI　filter　design　achieve　the　expected　IL　and　achieve　good　noise　suppression　effect,　it　is　necessary　to　consider　the　impact　of　noise　source　impedance.　The　voltage　insertion　loss　method　can　only　calculate　the　maximum　and　minimum　values　of　the　amplitude　of　the　noise　source　impedance,　and　cannot　solve　the　phase　of　the　noise　source　impedance.　To　solve　the　above　problems,　this　paper　proposes　a　noise　source　impedance　extraction　method　based　on　inserting　passive　two-port　network　without　adding　experimental　equipment.　Combined　with　experimental　measurement　and　theoretical　calculation,　the　accurate　values　of　the　amplitude　and　phase　of　the　noise　source　impedance　are　obtained.　First,　insert　three　different　passive　two-port　networks　between　the　equipment　under　test　(EUT)　and　the　linear　impedance　stabilization　network　(LISN).　Secondly,　the　equivalent　circuit　of　noise　source　impedance　extraction　is　established,　and　then　the　binary　quadratic　equations　about　the　real　part　and　imaginary　part　of　the　noise　source　impedance　are　established　according　to　the　equivalent　circuit.　Finally,　through　the　programming　of　the　mathematical　software　platform,　the　binary　quadratic　equations　corresponding　to　each　frequency　point　are　solved　automatically　and　circularly,　and　the　effective　frequency　points　measured　experimentally　in　the　conducted　EMI　test　frequency　band　(9kHz～30MHz)　are　selected,　so　that　the　real　and　imaginary　parts　of　the　noise　source　impedance　can　be　obtained,　and　then　the　accurate　calculation　of　the　amplitude　and　phase　of　the　noise　source　impedance　can　be　realized.　The　experimental　results　show　that,　no　matter　the　common　mode　(CM)　noise　source　impedance　or　the　differential　mode　(DM)　noise　source　impedance,　most　of　the　amplitudes　of　the　noise　source　impedance　calculated　by　the　proposed　method　fall　between　the　maximum　and　minimum　values　of　the　amplitudes　of　the　noise　source　impedance　calculated　by　the　voltage　insertion　loss　method　in　the　conducted　EMI　test　frequency　band　(9kHz~30MHz),　which　further　improves　the　calculation　accuracy　of　the　amplitude　of　noise　source　impedance.　In　addition,　the　proposed　method　can　also　obtain　the　exact　phase　of　the　noise　source　impedance,　which　is　not　available　in　the　voltage　insertion　loss　method.　Finally,　the　noise　current　predicted　by　the　proposed　noise　source　impedance　extraction　method　is　compared　with　the　noise　current　actually　measured　when　the　LED　driver　is　working.　The　experimental　results　show　that　the　two　are　in　good　agreement,　which　further　verifies　the　correctness　and　effectiveness　of　the　proposed　noise　source　impedance　extraction　method.　The　following　conclusions　can　be　drawn　from　the　experimental　analysis:　①　Compared　with　the　voltage　insertion　loss　method,　the　amplitude　of　noise　source　impedance　calculated　by　the　proposed　method　has　higher　accuracy,　and　the　phase　of　noise　source　impedance　can　also　be　obtained.　②　At　the　same　time,　the　noise　source　impedance　calculated　based　on　the　proposed　method　can　accurately　predict　the　noise　current　of　LISN　after　inserting　EMI　filter,　which　provides　a　theoretical　basis　for　designing　high-performance　EMI　filter.　③　The　proposed　method　has　the　advantages　of　low　cost,　simple　operation,　strong　practicability　and　universal　applicability.　©　2023　Chinese　Machine　Press.　All　rights　reserved.