Abstract: To address the issue of limited dynamic evaluation methods for simply supported girder bridges under moving loads and the time-consuming nature of traditional dynamic load test measurements, this study focuses on a simply supported girder bridge and presents a method to dynamically assess its reaction to mobile loads. The proposed method involves creating a precise vehicle-bridge coupling model, validating it through dynamic displacement measurements using millimeter wave radar, modal analysis, and dynamic load tests. Furthermore, the influence of unevenness on bridge decks and the speed of vehicles on the factor of deflection impact on bridges is examined and compared with current standards. Results indicate that the deflection impact coefficient peaks at a certain vehicle speed and varies across different beam spans, and increases significantly as bridge deck grade deteriorates. The deflection impact factor's relationship with the fundamental frequency of the bridge differs from what is specified. Millimeter wave radar has proven to be an effective non-contact testing method for measuring complex bridge vibrations. The conclusions drawn from this study can offer valuable insights for future dynamic evaluation methods and maintenance of simply supported beam bridges with small to medium spans.