Abstract: Response surface methodology was used to study the laser edge sealing welding of 2A12 aluminum alloy. The results showed that the main influencing factors of the geometrical characteristics of 2A12 aluminum alloy were defocusing amount, welding speed and laser power. From fusion line to weld center, the microstructure of 2A12 aluminum alloy laser edge sealing weld were coarse cellular dendrites, fine cellular dendrites and equiaxed crystals. The strengthening phases distributed along the grain boundary near the fusion line and in the transition region. At the center of weld, a small amount of strengthening phases distributed in the grain. Compared with the positive defocusing amount, the grain size of weld was larger and the magnesium element burned more seriously at the negative defocusing amount, which reduced the content of strengthening phase CuMgAl₂ and led to the weakening of strengthening effect and the reduction of weld microhardness. When defocusing amount were + 2 mm and −2 mm, both of the air tightness of laser edge sealing welding were good.