The invention discloses a double-way friction stir welding method for dissimilar material mismatching processing. The problems are solved that in the butt joint and friction stir welding process of dissimilar metal such as aluminum/steel, aluminum/copper and magnesium/copper, the situations easily exist that a stirring head is abraded, formation of welding seams is poor due to a material glued tothe stirring head, and the defects exist in intermetallic compounds in the welding seams and exist in the welding seams. The method comprises the steps that 1, two parent materials to be welded are preprocessed, the thickness of a welding area is subjected to differentiation, and a mismatching connector is formed; 2, firstly, the parent materials to be welded are subjected to ultrasonic cleaning and preprocessing, and then acetone is used for wiping the surfaces of the parent materials; 3, the two parent materials to be welded are clamped and located; 4, the stirring head with a large-sized shaft shoulder is shifted to the sides of the low-melting-point parent materials, a small quantity of high-melting-point parent materials are inserted in the stirring head, and first-time welding is conducted; 5, the stirring head is replaced by a small-sized stirring head, the small-sized stirring head is further shifted to the sides of the low-melting-point parent materials, second-time repair welding is conducted, and accordingly the good-quality connection between dissimilar materials is formed. The double-way friction stir welding method is applied to butt joint and friction stir welding ofthe dissimilar metal such as aluminum/steel, aluminum/copper and magnesium/copper.