Abstract: Microstructures and mechanical properties of friction-stir welding joint of 7A09 aluminum alloy thick-sheet were investigated.The results show that compared with base metal,the microstructures in the nugget contains fined,equiaxed grains,that transverse speed and rotational speed can affect the size of grains,that the precipitation phenomena in different zone are affected by welding heat.The profile of hardness traverse across the weld exhibits like W and that the heat-affect zone(HAZ) has serious softening.The result of tensile properties shows that the transverse tensile strength of FSW joint can reach about 70% of that of the base metal which fractures at heat-affected zone while transverse speed and rotational speed are optimized.