The concrete-filled steel tubular structureshave been widely employed in the super high-rise buildings,while the cavity defect inthecorewill seriously affectthe mechanical behaviorof the components. In this study, the action mechanism of the core concrete cavity defect detection technology based on the piezoelectric impedance is intensively investigated by suing the numerical simulation method.By comparing the calculation results of impedance with and without defect region, the position of defect is analyzed and determined, and the rootmeansquare of deviation damage index is defined to evaluate the damage degree at the detecting point.The results show that the existence of core concrete cavity defects will lead to a significant change in the impedance frequency curve of the embedded piezoelectric sensor in the corresponding position, and the defined damage index can effectively identify the cavity defects of the core concrete. The effectiveness of the core concrete cavity defect detection technology based on the piezoelectric impedance method is successfully verified by the numerical simulation method.