The　formation　process　of　interface　Kirkendall　voids　is　accompanied　by　the　formation　and　diffusion　of　vacancies,　so　the　behavior　can　not　be　ignored　during　interfacial　diffusion　and　void　formation　process.　In　this　study,　the　diffusion　process　of　Cu-Sn　interface　and　the　effect　of　vacancies　on　diffusion　in　Cu/Cu3　interface　were　investigated　using　molecular　dynamics　simulation.　Moreover,　the　diffusion　behaviors　of　atoms　were　analyzed,　while　the　vacancy　formation　energy,　diffusion　energy　barrier　and　vacancy　diffusion　activation　energy　were　obtained.　By　comparison,　it　was　found　that　the　models　containing　vacancies　more　easily　formed　diffusion　than　the　models　without　vacancies.　In　addition,　the　formation　energy　of　Cu　vacancy　in　the　Cu　crystal　was　greater　than　that　in　Cu3Sn　crystal.　The　formation　energies　of　Cu1　vacancy　and　Cu2　vacancy　were　close　to　each　other　in　Cu3Sn　crystal,　and　they　were　both　smaller　than　the　formation　energy　of　Sn　vacancy.　Furthermore,　the　vacancy　diffusion　barrier　and　vacancy　diffusion　activation　energy　of　the　Cu/Cu3Sn　interface　were　calculated.　The　results　showed　that　the　vacancy　diffusion　activation　energy　of　Sn　was　higher　than　that　of　Cu.　©　2018,　Editorial　Board　of　Transactions　of　the　China　Welding　Institution,　Magazine　Agency　Welding.　All　right　reserved.