Abstract: Crack damage results in reduction of structural local stiffness, which is closely related to the change of structural natural frequencies. Strain energy is more sensitive to local damage than natural frequencies. Strain energy change is used as damage index and a nondestructive crack detection method is proposed. The damage index is influenced by several factors. The detection results are verified through parameter hypothesis testing. Modal experiments of a simply supported beam with crack damage were performed, the predamage and postdamage data are extracted, and used to identify crack damage location and dimensions. It is shown that the results obtained using the damage detection method are accurate, and the method is applicable to crack damage detection.