Abstract: The application of MUSIC algorithm in plate-like structures was investigated, and a damage factor based on the characteristic value of the MUSIC algorithm was proposed, which provided a reliable damage level assessment theory for plate-like structure damage imaging technology based on the MUSIC algorithm. The correlation between high-precision eigenvalues calculated by the MUSIC algorithm and amplitudes of Lamb wave damage scattering signal was used. The various damage levels were simulated by using the Abaqus finite element software. After the damage was imaged and localized in the plate-like structure, the structural damage level was transformed into the amount of eigenvalue change according to the scattering signal amplitudes, and the damage factor was calculated according to the eigenvalues. A damage evaluation model was established to predict the damage level and the correctness of the model was verified through experiments. Experimental results showed the proposed eigenvalue-based damage factor responded well to the damage level as the damage level increased linearly with the increase of the eigenvalue damage factor under the appropriate excitation frequency. The method, which can effectively reflect the structural damage level within a certain range, had high accuracy and stability, improving the structural damage detection technology based on the MUSIC algorithm.