—　Eddy-current　(EC)　testing　is　one　of　the　contactless　nondestructive　testing　techniques　for　the　physical　property　measurement　(e.g.,　thickness,　electrical　conductivity,　and　magnetic　permeability)　of　steel　plates　in　various　industrial　applications.　In　this　study,　an　estimation　method　of　plate　thickness　and　permeability　is　proposed　using　the　triple-frequency　coil　inductance　with　probe　lift-off.　The　functional　relationship　between　the　plate　properties,　probe　lift-off,　and　characteristics　of　coil　inductance　is　indicated　by　the　simplified　analytical　model,　which　is　employed　for　the　initial　guesses　of　optimization.　The　proposed　method　can　decrease　the　influence　of　the　local　minimum　on　property　estimation.　Numerical　simulations　and　experiments　have　been　performed　to　evaluate　the　proposed　method　with　various　plate　properties　and　probe　lift-off.　Compared　with　the　estimation　results　without　the　appropriate　initial　guesses,　the　proposed　method　is　more　robust　and　accurate　for　various　cases,　with　a　relative　estimation　error　smaller　than　8%.　©　2023　IEEE.　Personal　use　is　permitted,　but　republication/redistribution　requires　IEEE　permission.