The　harmonic　decomposition　method　was　introduced　to　illustrate　the　current　reduction　mechanism　of　coupled　inductor　in　VRM　(voltage　regulator　module).　AC　winding　loss　of　flyback　transformer　was　decomposed　into　transformer　component　loss　and　inductor　component　loss.　It　was　just　the　inductor　component　ripple　that　took　the　main　role　for　winding　loss　due　to　severe　air　gap　fringing　effect,　especially　in　low　and　middle　power　supply.　Therefore,　based　on　multiphase　coupled　inductor　technique　and　winding　loss　features,　magnetic　integration　of　multiphase　interleaving　flyback　converter　was　proposed　to　reduce　current　ripple　and　improve　the　inductor　component　winding　loss　and　core　loss.　Theoretical　analysis　and　experiment　were　carried　out　for　verification.