Abstract: Based on an old reinforced concrete arch bridge, which has been in-service for about 40 years, a scaled one-span bridge model was fabricated with organic-glasses. Notches were made on the arch ribs to simulate the damage. Dynamic experiments were conducted on the undamaged and damaged models. Dynamic properties of the arch bridge were obtained. Wavelet packet analysis was utilized to identify the damage state of the arch bridge. It is discovered that the wavelet packet component energy is sensitive to the abnormal state of the arch structure. It can also be drawn that the wavelet component energy can be used as a damage index for the damage diagnosis of arch bridge.