Isolated　power　converters　are　widely　used　for　its　safety　and　flexible　adjustment　between　input　and　output　voltage　range.　EMI　occurs　due　to　the　presence　of　switching　process.　The　existence　of　parasitic　parameters　in　transformers　causes　the　work　of　EMI　prediction　in　isolated　DC-DC　power　converters　more　complicated.　Parasitic　parameters　in　transformer　are　the　crucial　propagation　paths　for　CM　noise　conduction.　For　improving　the　accuracy　of　EMI　prediction,　this　paper　developed　a　wide-band　frequency　transformer　model　based　on　the　two-capacitance　model,　further　considering　both　the　effect　capacitive　and　inductive　coupling　on　conductive　common　mode　noise.　Furthermore,　the　influence　of　permeability　versus　frequency　of　Mn-Zn　ferrite　on　CM　transmission,　is　investigated　in　detail.　Two-port　measurement　is　used　for　the　validation　of　the　proposed　high　frequency　model.　The　experiment　results　demonstrate　that　the　proposed　wind-band　frequency　transformer　model　can　well　predict　the　CM　noise　behavior　in　the　frequency　range　of　100　kHz　to　100　MHz.　©　2025　China　Power　Supply　Society.　All　rights　reserved.