Abstract: The butt joints of 7050 aluminum alloy plates with thickness of 6.3 mm were obtained by friction stir welding with optimizal parameters,and the microstructure and impact toughness of the joints were analyzed.The results indicate that refined equiaxed grains could be observed in weld nugget zome (WNZ) and shoulder affected zone (SAZ) of the joint while coarse grains were found in heat affected zone (HAZ).Thermo-mechanically affected zone (TMAZ) on advancing side consisted of highly deformed grains,and small deformation in retreating side.The microhardness of the joint showed pattern of W-shape,which was low in HAZ and TMAZ but high in base metal and WNZ,and the microhardness of WNZ presented an ascending trend from bottom to top.The impact toughness of the welded joint was superior to the base metal.Lots of dimples existed in the substrate impact fracture,WNZ and HAZ,which showed a typical ductile fracture characteristic.