Abstract: Through the friction stir lap welding test of 5083 and 7005 dissimilar aluminum alloys with a thickness of 2 mm, the influence of process parameters on the interface characteristics and mechanical properties of the joint was analyzed. The results show that there are hook like defects and incomplete breakage in the lap joint due to downward migration of the interface. The downward expansion of hook like defects reduces the effective plate thickness of the bottom plate, thus deteriorating the joint performance. The incomplete breakage of the interface reduces the effective lap width of the bonding interface, reduces the effective stress area of the interface, thus reduces the joint strength. Only when the effective plate thickness and the effective lap width are increased at the same time, the joint strength can be high. With the increase of welding speed, the tensile shear strength of the joint increases first and then decreases. There are two fracture modes of the joint: tensile fracture along the bottom plate at retreating side and shear fracture along the bonding interface.