The　effects　of　both　electric　energy　storage　and　common-mode　(CM)　Electro　Magnetic　Interference　(EMI)　noise　emission　of　high-frequency　transformer　are　analyzed　considering　the　voltage　distribution　in　transformer　windings.　One-port　terminal　capacitance　is　used　to　present　the　electric　energy　storage　behaviors,　while　two-port　network　transfer　capacitance　is　used　to　present　the　CM　EMI　noise　behaviors.　The　calculation　methods　are　also　proposed　for　the　two　capacitances.　Based　on　this　understanding,　a　new　transformer　model　is　built　which　can　describe　both　the　electric　energy　storage　and　CM　EMI　noise　behaviors　of　a　transformer　in　one　model.　The　model　can　also　explain　the　CM　EMI　noise　mechanism　clearly　and　rationally.　Finally,　the　experiment　and　simulation　verify　the　theoretical　analysis　and　the　model.