Due to its location in the Alpine-Himalayas seismic belt, Iran suffers from many earthquakes in different parts of the world every year. During the earthquake, bridges are becoming more and more important in transportation matters. Considering the importance of this type of structures, predicting the reaction and performance of bridges under earthquake is of particular importance. In recent years, the dynamic response of cable bridges has been very much considered. Cables carry loads from deck to towers and inherently have nonlinear geometric behavior. Seismic response of cable bridges depends considerably on linear or nonlinear analysis. In researches, the equivalent elastic modulus is generally used to model nonlinear geometric behavior of cables. In this paper, analytical results and observations of the dynamic response of the suspended bridge are presented. Observations are based on induction vibration tests of traffic and the environment, which allows the extraction of dynamic characteristics of the structure in terms of resonance frequencies, modal shapes and damping.