A large number of built small and medium-span bridges in China are facing the problem of increasingly degrading structural performance. Therefore, it is of great significance to carry out lightweight intelligent monitoring and realize damage identification and early warning, so as to ensure the safe operation of these bridges. For typical small and medium-span simply supported beam bridges, a damage analysis method based on measured dynamic deflection data was established by combining the influence line theory and mechanical constitutive equations. Furthermore, based on the high-precision monitoring algorithm and instruments of digital image correlation (DIC), the real-time dynamic deflection data of the bridges were obtained. It is shown that typical defects such as sectional stiffness degradation, hinge joint damage and failure, and support performance degradation are effectively identified. The results were applied to the digital transformation project of an overpass in Shanghai, which verifies the effectiveness of the dynamic deflection DIC optical measurement technology and the damage identification method and indicates that the proposed method has good value in popularization and application.