Abstract: Adopted the advantages of laser welding and by use of ANSYS software,the structure of the Al-50Si shell and the cover (4047 aluminum alloy) of the multi-chip subsystems which sealed by laser welding was analyzed,and the physical verification was also carried out. It was proved that structure form is the key factor which affected the quality of multi-chip subsystems which sealed by laser welding,the stress in laser weld of square structure is 36% higher than that in special-shaped structure (according to ANSYS analysis results),and the air tightness of the square structure is lower by almost one order of magnitude than that of special-shaped structure,which performed by physical verification. The reason is that after laser welding,the welding cracks induced by welding stress in the weld of square structure, so as to affect the air tightness of the weld. By adopt of specialshaped structure of multi-chip subsystems made from Al-50Si composite materials and the cover made from 4047 aluminum alloy, the stress in the welds can be effectively reduced,so the cracks in the weld are actually avoidable during laser welding. The result was indicated that the helium leak rate of the weld of special-shaped structure can reach to 8.9×10^-9 Pa·m³/s, which met the hermetic package requirement of multi-chip subsystems.