Abstract: When the vibration method is employed to detect internal defects in concrete, the frequency composition of the vibration feedback signal is complex, featuring strong non-stationary frequency variation and nonlinear characteristics. Consequently, traditional time-frequency domain analysis methods find it difficult to identify defects from the waveform. With the aid of fractal theory, an impact vibration test is conducted on the concrete structure model with defects, and the potential relationship between the box dimension of the vibration feedback signal and the internal defects of concrete is analyzed. Experimental studies reveal that under the excitation of a magnetically induced shock source, by observing the box dimension value of the vibration feedback curve on the surface of the concrete structure, the specific location of voids inside the concrete can be inferred. The experimental results offer a new detection concept for large-scale surveying of the internal compactness of concrete structures.