Abstract: 2A12 aluminum alloy shell lugs fracture failure occurred during system separation test, and chemical compositions analysis, metallographic examination, fracture analysis and spectrum analysis were done to the fractured shell lugs to find the fracture reason. The results show that the fracture of the shell lugs was typical woody fracture and the fracture originated from the surface gathered undissolved compounds. The main reason for the fracture was that the extrusion deformation and the quenching heating temperature were not enough, which result in a great deal of as-cast network structure and undissolved compounds in microstructure and reducing strength and ductility of the shell lugs.