Metalized　film　capacitor　is　widely　used　in　compensation　networks　for　magnetic　resonant　wireless　power　transfer　(WPT)　system.　As　an　essential　design　parameter,　equivalent　series　resistance　(ESR)　of　film　capacitors　will　cause　severe　heating　and　shorten　the　life　of　the　capacitor　during　operation.　In　this　paper,　the　loss　model　is　proposed　by　analyzing　the　loss　mechanism　of　the　film　capacitor.　Based　on　the　measured　data　of　KEMET　R76　series　film　capacitors,　the　relationship　between　the　tangent　of　loss　angle　($\text{tan}\!\delta$)　and　operating　frequency　and　capacitance　is　analyzed,　then　the　calculation　model　of　ESR　is　proposed.　Finally,　the　calculated　value　is　compared　with　the　measured　value　to　prove　the　calculation　model＇s　correctness　and　feasibility,　which　is　very　important　to　optimize　the　loss　of　compensation　network　and　WPT　system.　©　2022　IEEE.