In　the　development　of　switching　power　supply,　electromagnetic　interference(EMI)　should　be　much　attended.　This　paper　investigated　the　transmission　mechanism　of　conducted　common-mode(CM)　noise　in　a-single-switch　forward　converter.　Based　on　the　analysis,　a　CM　transmission　mode　can　be　built.　Through　theory　analysis,　methods　of　designing　circuit　structure　and　transformer　construction　can　improve　CM　noise.　Experimental　results　validated　the　proposed　model　and　the　developed　CM　noise　reduction　techniques.　©　2022　IEEE.