Harmonic　magnetic　field　focus　detection　technology　has　been　utilized　for　in-service　pipeline　defect　detection　due　to　its　advantage　in　providing　high-sensitivity　and　noncontact　detection.　However,　this　technology　encounters　interference　from　background　signals　and　noise　during　high　lift-off　detection,　which　limits　the　accuracy　of　defect　signal　extraction.　To　quickly　and　robustly　identify　pipe　defects,　this　work　discloses　a　novel　defect　signal　extraction　method　for　multiple-harmonic　magnetic　field　detection　technology.　The　proposed　method　is　insensitive　to　noise　interference,　effectively　extracting　defect　signals　even　under　high-intensity　noise　conditions.　A　pipe　defect　model　based　on　magnetic　dipole　moments　is　established　for　simulation　analysis,　and　a　pipeline　test　platform　is　built　for　experimental　validation.　The　results　demonstrate　that　the　proposed　method　can　identify　defects　from　signals　with　a　low　signal-to-noise　ratio　of　5.7　dB　and　locate　pipes,　welds,　and　defects　with　high　resolution.