In　this　study,　a　harmonic　magnetic　field　detection　technology　is　proposed　in　order　to　detect　the　damage　of　an　in-service　coated　steel　pipeline.　Based　on　the　electromagnetic　theory　and　magnetic　field　detection　principle　integrated　with　magnetic　focusing　technology,　an　array　consisting　of　focusing　detection　probe　and　harmonic　magnetic　field　detection　system　was　designed.　Numerical　simulations　for　different　coil　structures　was　performed　by　finite　element　simulation　technique　to　explore　the　focusing　performance　of　designed　coil　structure.　The　feasibility　of　the　detection　probe　and　harmonic　magnetic　field　detection　technology　was　verified　by　experimental　results　and　numerical　simulations.　The　results　of　this　study　show　that　the　proposed　method　can　provide　excellent　information　about　the　full　wall　thickness　by　penetrating　the　cladding　over　the　surface　of　pipeline　and　effectively　identify　the　outer　wall　defects　and　the　inner　wall　corrosion.　(C)　2020　Elsevier　Ltd.　All　rights　reserved.