A series of experiments is carried out on the characteristics at the wedge bond interface. Bond lift-off characteristics are studied by using Scanning Electron Microscope with EDS-test. The characteristics of input impedance of PZT transducer are analyzed by the driving electric signal measured by Oscilloscope. Results show that the pattern of partially bonded material at the interface of ultrasonic wedge bonds exposed by peeling underdeveloped bonds simulates a torus with an unbonded central region. For the same machine variables, the input impedance and transforming power of the first wedge bond are greater than that of the second wedge bond. Some conclusions drawn by analyzing the input impedance and the power of PZT consist with the results gotten by testing microstructures at the interface.