Abstract: 5A06/2219 aluminum alloy was welded by 1070,4043 and 4047 filler wires with different Si content,respectively,and the influences of Si content on the welding crack sensitivity were studied. The microstructure and crack fracture of different welding joints were observed by optical microscopy（ OM）,scanning electron microscopy（ SEM） and energy spectrum analysis（ EDS）,and the crack initiation of dissimilar aluminum alloy welded joints was discussed. Compared with the welded joint obtained by 4047 filler wire,the obvious cracking tendency can be found in dissimilar welded joints obtained by 4043 and 1070 filler wire. The welding crack belongs to solidification crack and Cu Al₂ eutectic phase plays a dominant role in crack initiation process.