_{:A new type Al-Zn-Mg-Cu alloy Al-Mg alloy was welded using Tungsten Inert Gas welding method. Microstructures and microhardness of the joint were analyzed. The relationship between the temperature and microstructure and microhardness were established based on the simulation result of the temperature fieldthrough the Visual-weld.At last, the residual stress was employing the X-ray diffraction method. The results showed that microstructure in the weldseam shown as corase equiaxed grain zone(EQZ). That zone closed to fusion line was an equiaxed grain zone with small size, whichis ascalled Fine-Grain Layer. For the Fine-Grain layer, microstructure showed epitaxial solidification morphology. However, partial grain boundary re-melt appears outside of fusion line. Residual stress in the weldment is small and has the same distribution in the stable forming segment of weldseam. However, it has an inverse distribution in the front end of weldseam. With the influence of temperature curve of welding and η phase, microhardnesses in the hot affect zone is bigger than that in other zones in the weldment.Keywords:Butt-weld of MIG; Al-Zn-Mg-Cualloy; residual stress; microtopography; microhardness}