Electromechanical impedance approach infers the structural dynamic characteristics at relatively high frequencies by using self-sensing piezoelectric wafer elements. Structural damage can be detected by comparing structural dynamic responses of damaged and undamaged structures. This paper presents an ongoing effort using piezoelectric wafer sensors to measure structural electro-mechanical impedance response under tensile loading and quantitatively correlate the measurements with damage progression. The purpose is not only to develop a better understanding of the damage progression in composite materials, but also to establish a relationship between electromechanical impedance measurements with local material damage progression. Multi-physics finite element codes are used to simulate the electromechanical resonance of a free piezoelectric wafer sensor to better understand the effect of electromechanical transduction. The effects on impedance measurement from bonding layer degradation and PWAS degradation are also studied. Our study confirms that the EMI changes are related to very small amount material or structural changes, indicating that electromechanical impedance spectroscopy offers a potential for detection of the progression of small damage at the material level.