In this study, sheets of a new Al-Zn-Mg-Cu alloy have been welded using automatic TIG welding with filler wire. The microstructure characteristics and mechanical properties of weld joints were analyzed. Results showed that the fusion zone (FZ) is comprised of non-dendritic equiaxed grain zone (EQZ) and coarser dendritic equiaxed grains, and the fusion boundary does not appear to nucleate epitaxially from the heat affected zone (HAZ) substrate, the compound T (AlZnMgCu) phase precipitates discretely on grain boundaries; the HAZ is divided into the solid solution zone that is close to the FZ and overaging zone which is farther away from the FZ because of an alteration of the strengthening precipitates, they possess different microhardness values, grains in the HAZ are elongated as same as the base metal (BM) and not coarser compared with the BM; The minimum microhardness of the joint is obtained in the FZ and the value is approximately 120HV, and that of the BM is about 184HV, the ultimate tensile strength of joints is 421.75MPa which is 65.08% of that of the BM, samples of the tensile test fracture at the FZ and the fractured surface is ductile fracture characteristics, small particles whose composition is almost same with the compound T phase are observed at the bottom of dimples.