Abstract: Aimed at the problem of gas leakage of the package box used for filter, SEM and EDS were used to compare and analyze the different microstructure and element composition between the qualified and failure package box samples, and the failure causes were discussed. The results showed that the high concentration silicon was precipitated on the surface of aluminum alloy package box mostly in the flake and granular forms. That resulted in stress concentration, reduced the fusion performance of liquid metal welding and metal density in fusing zone, and eventually led to microcracks and welding defects. The improvement measures were proposed based on the results at last.