Using　our　homemade　tensile　device　inside　a　transmission　electron　microscope,　we　in-situ　investigated　the　deformation　behaviours　of　the　nano-twinned　nanocrystalline　Au　thin-films　with　thickness　of　similar　to　15　nm　and　average　grain　size　of　similar　to　16　nm.　Our　extensive　in-situ　observation　studies　reveal　that　the　deformation　of　the　nano-twinned　nanocrystalline　Au　thin-film　was　dominated　by　the　cooperative　grain　boundary　sliding　and　migration,　which　were　rarely　observed　in　the　previous　reports.　Meanwhile,　our　statistic　shows　that　the　nano-twins　tended　to　promote　further　stress-driven　grain　growth,　and　the　promotion　became　more　remarkable　for　the　nano-twinned　grains　that　were　located　at　the　crack　tips.　(C)　2020　Published　by　Elsevier　Ltd　on　behalf　of　Acta　Materialia　Inc.