Analytical instruments such as optical microscope, SEM and TEM are employed to investigate and analyze the microstructure and characteristics of soldering joint interfacial region. The results indicated that interactive crystallization exists in part of the interfacial region by using a newly developed kind of soldering filler metal. The composition of the interfacial region is complex such that both solid solution of Cd,Sn,Zn and small amounts of fine grained compounds of Mg2Sn,MgZn exist. Solid solution can improve the strength and plasticity, and small amounts of fine-grained compounds can strengthen the matrix which is beneficial for improving the bonding strength. However, successive laminate structure of intermetallic compounds will result in embitterment and deteriorate the properties of the joint.