New　Al-Zn-Mg-Cu　alloy　sheets　have　been　welded　using　automatic　TIG　welding　with　filler　wires.　The　microstructure　characteristics　and　mechanical　properties　of　weld　joints　were　analyzed.　Results　show　that　the　fusion　zone　(FZ)　is　comprised　of　a　non-dendritic　equiaxed　grain　zone　(EQZ)　and　a　coarser　dendritic　equiaxed　grains,　and　the　fusion　boundary　does　not　nucleate　epitaxially　from　the　heat　affected　zone　(HAZ)　substrate,　and　the　compound　T　(AlZnMgCu)　phase　precipitates　discretely　on　grain　boundaries.　The　HAZ　is　divided　into　a　solid　solution　zone　that　is　close　to　the　FZ　and　an　overaging　zone　which　is　farther　away　from　the　FZ　because　of　an　alteration　of　the　strengthening　precipitates,　resulting　in　different　microhardness　values,　and　the　grains　in　the　HAZ　are　elongated　as　same　as　the　base　metal　(BM)　and　they　do　not　become　coarser　compared　with　the　BM.　The　minimum　microhardness　of　the　joint　is　obtained　in　the　FZ　and　the　value　is　approximately　HV　1200　MPa,　and　that　of　the　BM　is　about　HV　1840　MPa,　and　the　ultimate　tensile　strength　of　joints　is　421.75　MPa　which　is　65.08%　of　that　of　the　BM.　Samples　of　the　tensile　test　fracture　at　the　FZ　and　the　fractured　surface　is　of　ductile　fracture　characteristics.　Small　particles　whose　composition　is　almost　same　as　the　compound　T　phase　are　observed　at　the　bottom　of　dimples.