The relationship between excitation voltage of lead zirconate titanate piezoelectric ceramic (PZT) sensor and testing sensitivity of electro-mechanical impedance (EMI) based structural health monitoring method is quantitatively studied. The specimen used in this study is aluminum beam structure with the size of 1250mm×100 mm×3mm. Three hole damages with the diameters of 1.2, 2.5 and 3.5mm are drilled at 1 000mm from the PZT center. The sensitivity of EMI method is investigated at 8 kinds of excitation voltages from 0.01 to 20 V, with WK 6500B precision impedance analyzer and self-established high excitation voltage electric impedance measurement system (HEVEIMS). The results show that the relation between excitation voltage and EMI sensitivity is not monotonic. In the voltage range of 1-10 V, the sensitivity of EMI method increases significantly with the increase of excitation voltage. The increasing of non linear signals in PZT electric impedance spectrum at high excitation voltage is the main reason for the increase of EMI sensitivity. This study not only gives a reference for the selection of excitation voltage, but also provides a data support for the clarification of the relation between excitation voltage and EMI sensitivity.