At present, there is a lack of research on the selection of PZT size and bonding location during the application of electro-mechanical impedamce technique. The influence of size and bonding location of PZT on the sensor admittance is investigated by designing the comparative experiment. The results show that the local peaks containing the information about the measured structure mainly occur around the resonance frequency bands. The larger the PZT size, the stronger the local dense peaks at the resonant frequency bands. The size selection in the electro-mechanical impedamce technique should have a combination of frequency range selection which should include resonance frequency bands. The bonding locations have an influence on the distribution of the local peaks in the admittance curve. The study results provide a reference for the size selection and bonding location determination of PZT in the application of the electro-mechanical impedamce technique.