For　inductors,　such　as　DC　chokes,　PFC　inductors,　resonant　inductors　and　fly-back　transformers,　magnetic　field　distributions　in　winding　windows　are　extremely　complex　due　to　the　air-gap　fringing　effects　in　the　core.　Existing　high-frequency　winding　loss　calculation　method　usually　ignores　the　fringing　effect　losses　caused　by　air-gap　fringing　fluxes,　resulting　much　errors　for　winding　loss　analysis　and　loss　reduction　designs.　In　this　paper,　an　improved　winding　loss　theoretical　calculation　method　of　gapped　inductor　is　proposed.　By　replacing　the　air-gap　magnetic　voltage　drop　with　equivalent　surface　current　sheet　with　certain　shape　and　certain　current　density　distribution　near　the　air-gap,　the　winding　loss　accuracies　were　improved.　And　then　mirror-image　method　was　used　to　equivalent　the　influence　of　the　boundaries　of　high　permeability　magnetic　core.　The　mirror　image　method　was　extended　to　dual　2D　model　approximation　of　3D　model.　©　2012　IEEE.