Abstract: Objective The aim is to explore the optimal friction stir welding (FSW) parameters, achieve high-quality butt-overlap welding of 7075/5A06 dissimilar aluminum alloy thin plates, and solve the problems such as weld thinning and hook defect existing in the welding of butt-overlap structure of dissimilar aluminum alloy thin plates. Methods A stepped-shoulder welding tool was utilized to achieve welding of butt-overlap structure of 1 mm AA7075-T6 and 2 mm AA5A06-O aluminum alloys. Results The results show that under the structure of this welding tool, welding process window is relatively wide. When rotational speed of stirring pin is 700～1 100 r/min and welding speed is 300 mm/min, sound joints could be achieved. Conclusion Under the parameters of 900 r/min-300 mm/min, influence of hook defects is eliminated, and tensile strength of joints reaches 335 MPa±11 MPa, reaching 94% that of 5A06-O base material.