Harmonic　magnetic　field　detection　for　pipes　has　the　merits　of　penetration　and　sensitivity.　However,　issues　like　the　probe＇s　shape,　limited　data　characterisation,　and　poor　targeting　restrict　the　detection　distance.　To　address　this,　a　novel　defect　detection　system　using　targeted　magnetic　moment　enhancement　and　targeted　magnetic　field　focusing　probe　and　its　spatial　distance　algorithm　is　proposed　to　detect　in-service　steel　pipe　damage.　The　excitation　coil　structure　is　designed　to　increase　the　effective　detection　distance　and　focus　the　diffuse　magnetic　field.　A　full　bridge　balanced　differential　circuit　control　steategy,　separate　from　the　detection　end,　is　adopted　to　extend　datacharacterisation.　Also,　a　spatial　distance　harmonic　inner　product　correlation　layer　resolution　matching　tracking　algorithm　is　proposed　to　alleviate　the　problem　of　the　insufficiently　targeted　characterisation　of　detection　data　using　harmonic　signals　under　real　acquisition　conditions.　Experiments　on　20#　steel　pipes　demonstratethat　the　system　can　discriminate　the　defect　severity　and　achieve　full　wall　thickness　detection.　It　shows　advantages　in　enhancing　detection　height　andidentification　clarity,　especially　useful　for　pipes　with　ultra-thick　claddings　or　larger　burial　depths　in　extreme　conditions,　thus　providing　a　new　approach　for　practical　engineering　detection.