Interleaved　fly-back　topology　is　widely　used　in　PV　micro-inverter　due　to　its　simple　structure　with　the　least　component　numbers.　However,　the　efficiency　in　the　fly-back　transformer　becomes　a　great　challenge　because　of　the　high　frequency　fringing　fluxes　near　the　air-gap　to　cause　great　AC　winding　losses,　especially　with　higher　operation　frequencies　for　increasing　the　power　density.　In　order　to　reduce　the　winding　losses　and　increase　the　power　density,　one　of　the　solutions　is　to　integrate　or　couple　the　two　fly-back　transformers　which　operate　in　phase-interleaved.　The　mechanics　of　the　magnetic　integration　in　reducing　AC　winding　losses　was　revealed.　The　model　for　winding　and　core　losses　were　built　and　the　factors　on　winding　and　core　losses　were　analyzed.　Simulation　and　experimental　results　validate　the　effectiveness　of　the　magnetic　integration　scheme.