A　new　type　Al-Zn-Mg-Cu　alloy　was　welded　using　Tungsten　Inert　Gas　welding　method.　Microstructures　and　microhardness　of　the　joint　were　analyzed.　The　relationship　of　the　temperature　with　microstructure　and　microhardness　was　established　based　on　the　simulation　result　of　the　temperature　field　through　the　Visual-weld.　At　last,　the　residual　stress　was　tested　by　the　X-ray　diffraction　method.　The　results　show　that　microstructure　in　the　weld　seam　is　a　coarse　equiaxed　grain　zone　(EQZ).　That　zone　close　to　the　fusion　line　is　an　equiaxed　grain　zone　with　small　size,　which　is　as　called　Fine-Grain　Layer.　For　the　Fine-Grain　layer,　microstructure　exhibits　epitaxial　solidification　morphology.　However,　partial　grain　boundary　re-melt　appears　outside　of　fusion　line.　Residual　stress　in　the　weldment　is　small　and　has　almost　the　same　distribution　in　the　stable　forming　segment　of　weld　seam.　However,　it　has　an　inverse　distribution　in　the　front　end　of　weld　seam.　With　the　influence　of　temperature　curve　of　welding　and　i　phase,　microhardness　in　the　hot　affected　zone　is　bigger　than　that　in　other　zones　in　the　weldment.