Al-Mg alloy plates with 10mm thick were welded by multipass MIG welding with the self-made wire as filler material, and microstructure of the welded joint were examined by metallographic, scanning electron microscope (SEM), X-ray diffraction and electron backscatter diffraction (EBSD). The results show that weld zone is typical of casting microstructure, and no obvious preferred orientation. Comparatively, grains are more inclined to epitaxial growth, and the texture in reheating coarse grain heat-affected zone is more obvious than fine grain layer and weld zone because of the comprehensive additive effect of welding thermal cycle and the structural similarity on the interface during multipass welding, grain growth is more apparent, microhardness is more low, and the residual stress value is only second to weld bottom, which is the weakest link.