Abstract: Diffusion bonding of magnesium alloy AZ31 and Al5083 was undertaken under an impact pressure in vacuum. The microstructural features,mechanical properties of the joints were investigated by scanning electron microscopy (SEM),energy Dispersive spectrometer(EDS),microhardness tester and x-ray diffractometer. The results show that the joints are formed four layers,such as magnesium alloy matrix,metallurgical reaction layer,diffusion layer and aluminum alloy matrix. There are the intermetallic compounds Mg₂Al₃,MgAl, Al_0.56Mg_0.44,and the highest hardness is 3 300 MPa in the joint zone. The tensile test results show that the tensile strength of the joint increases at first, then decreases,and an optimized bonding strength of up to 46MPa. The tensile fracture is mixture of quasi cleavage and dimple. There exists prevailing information asymmetry in the mg side and al side.