To　study　the　conducted　common-mode　(CM)　electromagnetic　interference　(EMI)　characteristics　of　a　single-switch　forward　converter　and　reduce　its　CM　noise,　the　analysis　of　the　transmission　mechanism　of　conducted　CM　noise　in　the　single-switch　forward　converter　is　necessary.　On　this　basis,　a　CM　noise　transmission　path　model　is　established,　and　a　calculation　method　is　proposed　to　determine　the　specific　external　capacitance　to　reduce　the　CM　noise.　In　addition,　aimed　at　the　defects　of　the　traditional　calculation　model　of　induced　charge　on　the　secondary　side,　an　improved　calculation　model　is　put　forward,　and　simulation　results　show　that　the　accuracy　of　the　improved　model　is　higher　under　ideal　conditions.　Afterwards,　the　balanced　winding　method　was　used　to　reduce　the　CM　noise　flowing　through　the　transformer,　and　a　prototype　of　single-switch　forward　converter　power　supply　was　used　for　experimental　verification.　Results　show　that　the　method　of　calculating　the　external　capacitance　was　effective,　and　the　accuracy　of　charge　calculated　by　the　improved　calculation　model　was　higher　when　the　windings　were　close　or　when　the　number　of　turns　per　unit　length　was　relatively　large.　©　2025　Editorial　Department　of　Journal　of　Power　Supply.　All　rights　reserved.