Abstract: Single-pass and double-pass welding were carried out on both sides of A7N01 aluminum alloy T-joint by metal inert-gas welding (MIG welding), respectively. The microstructure, microhardness and fatigue property of the joint were studied, and the influence of sing-pass and double-pass welding was analyzed. The results show that on the single-pass welding side, the microstructure was composed in order of fine grains, columnar grains and equiaxial grains, from fusion zone to weld center. The microstructure near fusion line on the double-pass welding side was similar to that on the single-pass welding side; near the interface between the two welds, columnar crystals were formed, and the columar crystals in the weld of the first pass was relatively coarse. Softening zone existed in base metal on both sides of the joint, and the softening degree on the single-pass welding side was more obvious. The joint by single-and double-pass welding on both sides, respectively, had a shorter fatigue life than the joint by single-pass welding on both side had; the fatigue crack originated on surface of the weld toe and propagated inside; the fracture presented a mixed fracture mode of quasi-cleavage fracture and ductile fracture.