Abstract: An engineering model between characteristic value of welding tool and specimen thickness was established based on heat input theoretical analysis of bobbing tool friction stir welding. According to this model, a welding tool was designed and optimized, which was used for join 2.5 mm thin-walled extrude profile of 6061-T6 aluminum alloy. Friction stir welding parameters were optimized as well. When the rotation speed of the tool was 1 000 r/min and welding speed was 600 mm/min, the joint obtained a maximum mechanical properties. The front side joint had a tensile strength of 231 MPa, 77% of the base material, and a bend angle of 180°, while the back side joint had a tensile strength of 226 MPa, 76% of the base material, and a bend angle of 180°.