Structural health monitoring based on electromechanical impedance is one of the methods for real-time monitoring and detection of structural damage using the coupling properties of piezoelectric materials. When a structure is exposed to corrosion, an electrochemical process is initiated and defects occur over the surface of the structure. In corrosion-prone structures, although a slight decrease in the mass is produced, it results in a significant decrease in its mechanical strength, integrity and fatigue life span. Therefore, the precise monitoring of structural health is important for detecting corrosion-induced surface defects and predicting the effect of corrosion on the mechanical properties and integrity of a structure. In this paper, the electromechanical impedance method is used to investigate the corrosion defect in the health monitoring of a cantilever beam and to identify and determine the factors affecting the damage index of corrosion. Experiments carried out to measure the impedance spectra on an aluminum beam, and a controlled acid corrosion has been imposed on the beam. The scalar damage index was used to quantify the defect. Empirical results obtained from experiments on cantilever beam show that factors like damage intensity, support positions and damage distance to the support location are effective on damage index caused by corrosion. The results show that there is a relationship between the support location and the damage location with the damage index. Also, it is observed that applied damage index as root-mean-square deviation of impedance has a direct relationship with the intensity of corrosion damage.