Eddy　-current　(EC)　testing　is　one　of　the　contactless　nondestructive　testing　techniques　that　has　been　frequently　applied　to　evaluate　the　defects　on　metallic　objects.　In　this　paper,　an　estimation　method　of　defect　depth　on　metallic　plates　is　proposed　based　on　the　approximate　analytical　model.　An　EC　coil　array　sensitive　to　various　defect　orientation　is　designed　to　scan　the　plate　surface.　The　independent　inductance　from　various　ferritecore　coil　pairs　can　be　found　by　the　approximate　analytical　model.　The　influence　of　defect　on　measurements,　including　depth　and　edges,　is　regarded　as　the　variation　of　probe　lift-off　in　the　tested　region,　defined　as　the　equivalent　lift-off.　Based　on　the　approximate　analytical　model,　when　defect　edges　have　relatively　smaller　influence,　the　defect　depth　on　the　plate　surface　can　be　approximately　obtained　by　estimating　the　equivalent　probe　lift-off　through　optimization.　In　numerical　simulations　and　experiments,　the　proposed　method　is　evaluated　by　testing　the　aluminum　and　stainless　-steel　plates　with　cracks　by　the　coil　array.　The　reconstructed　equivalent　lift-off　distribution　closely　relates　to　the　position　and　dimensions　of　defects　on　plates.