Elemental　migration　between　different　elements　is　intrinsic　process　for　diffusion.　Most　of　the　study　focused　on　the　presentative　shape　or　size　on　of　Kirkendall　pores,　yet　on　the　in-termediate　migration　process.　A　dynamic　elemental　transition　trajectory　recording　pro　-vides　realtime　diffusion　process　on　a　Cu-Sn　nanoscale　interface　is　thus　necessary　to　disclose　intermediated　reaction　on　diffusion　process.　In　this　work,　elemental　dynamic　diffusion　processes　were　recorded　and　analysed　on　a　microsize　Cu-Sn　couple　lamella　by　in　situ　transmission　electron　microscopy　up　to　Sn　melting　point.　Factors　of　atomic　quantity,　contact　condition　and　temperatures　were　studied　on　its　diffusion　behaviours.　The　work　shed　new　light　on　conventional　metallographically　interfaces　diffusion　and　provide　intrinsic　clues　for　solder　design.(c)　2023　The　Authors.　Published　by　Elsevier　B.V.　This　is　an　open　access　article　under　the　CC　BY　license　(http://creativecommons.org/licenses/by/4.0/).