Abstract: Germanium (Ge) is adjacent to Tin in periodic Table of the Elements;they are both in the main group Ⅳ and resemble each other in physical and chemical properties.A little element Ge was added into lead-free solder Sn2.5Ag0.7Cu (0.25, 0.5, 0.75, 1.0 wt%)and soldering interfaces were made up.The interfacial microstructure and photography were observed and analyzed with scanning electron microscope, the intermetallic compound thickness was measured with Auto CAD software, and interfacial composition was analyzed with energy dispersive X-ray analyzer.The results show that the pattern of IMC layer is pebble shape yet when adding element Ge, but displays a growth trend;the interface gets plainer and more regular with 150℃/100 h aging.The interfacial IMC layer is thicker with Ge in solder, but the ratio of getting thicker is smaller with 150℃/100 h aging.The addition of element Ge restrains the transformation of IMC Cu₆Sn₅ to Cu₃Sn and the growth during aging.