Due　to　increases　in　switching　frequency,　the　electromagnetic　interference　of　motor　drive　systems　has　been　receiving　more　attention.　In　a　motor　drive　system,　the　devices　in　the　inverter　produce　serious　electromagnetic　interference　during　high-frequency　switching.　It　is　necessary　to　model　the　motor　drive　system　to　predict　the　electromagnetic　interference　level.　Extraction　of　the　motor　impedance　characteristic　is　necessary　for　the　modeling　of　a　motor　drive　system.　At　present,　most　research　only　studies　the　measurement　method　of　a　motor　in　the　static　state.　However,　motor　impedance　characteristics　in　the　static　state　cannot　represent　motor　impedance　characteristics　in　operation.　In　this　paper,　an　online　measurement　method　of　motor　impedance　characteristics　is　proposed.　For　the　three-phase　asymmetric　circuit　caused　by　modulation,　the　motor　impedance　characteristics　in　operation　are　calculated　by　establishing　Kirchhoff　voltage　equations.　A　precision　power　scope　PX8000　is　used　to　measure　the　harmonic　components　of　single-phase　voltage,　single-phase　current,　and　common-mode　current.　The　time-delay　difference　of　the　precision　power　scope　PX8000　between　different　probes　is　also　considered.　Experiments　prove　that　the　time-delay　difference　does　not　affect　the　measurement　results.　Through　comparing　the　motor　impedance　characteristics　measured　by　different　filters,　the　method　of　extracting　the　motor　impedance　characteristics　online　is　validated.　Finally,　the　motor　impedance　characteristics　in　the　static　state　and　the　motor　impedance　characteristics　of　online　extraction　are　experimentally　compared.　The　motor　impedance　characteristics　of　the　online　extraction　method　proposed　in　this　paper　have　more　advantages　than　traditional　methods.