The　magnetic　core　is　an　important　part　of　the　magnetic　coupling　system　in　wireless　power　transmission　(WPT)　for　EVs.　It　helps　to　increase　the　coupling　coefficient　and　reduce　magnetic　field　leakage.　However,　it　also　brings　additional　core　loss.　While　the　traditional　core　loss　model　cannot　be　used　directly　due　to　the　uneven　distribution　of　the　magnetic　flux　density,　this　paper　focuses　on　the　flux　density　distribution　in　the　disk　core　of　a　WPT　system.　Based　on　a　finite　element　analysis　(FEA)　simulation　and　a　theoretical　magnetic　flux　density　distribution　analysis,　a　mathematical　model　of　magnetic　flux　density　distribution　is　built,　which　is　regarded　as　a　quadratic　function.　Through　this　model,　the　flux　density　distribution　can　be　calculated　by　the　electrical　and　mechanical　specifications　of　the　magnetic　coupling　system.　Combining　the　model　of　flux　density　distribution,　the　disk　core　loss　model　of　the　WPT　system　is　proposed—the　idea　of　which　is　dividing　the　disk　core　into　several　circle　sheets　firstly,　and　then　summing　the　core　loss　of　all　circle　sheets.　Finally,　the　FEA　simulation　results　verify　the　proposed　model　as　being　correct　and　flexible.　©　2021　by　the　authors.　Licensee　MDPI,　Basel,　Switzerland.