Abstarct: Bridges are counted as one of the most important and vulnerable structures in the vital veins of every country. The abundance of the concrete box deck bridges with horizontal arches on the one hand, and the complex dynamic behavior resulted from special geometric conditions of this class of bridges which have made them more vulnerable on the other hand, were aimed to be studied in this research. In this study, a model of a concrete box deck bridge with horizontal arches and the appropriateness of using lead-rubber bearing system were examined, and ultimately, two states of the bridge with and without seismic isolation were assessed by fragility curves, and the amount of possible seismic damage have been obtained. The study results were analyzed by modeling the bridge in the CSi Bridge finite-element software in three dimensions and under the excitation of 100 pairs of real accelerogram and under nonlinear time-history analysis, and the responses of the elements were extracted. So that, compared to the state without seismic isolator, the maximum relative displacement in the model with seismic isolator has decreased by 67 and 64 percent in the longitudinal and transverse directions; respectively. Also , baxsed on the result of modal analysis and comparison of the vibration period, the results show a significant increase in the first to third period of vibration of bridges in the state with seismic isolation compared to the without seismic isolation. The results of studies indicate that In this bridges with lead-rubber bearing system have reduced the drift of columns significantly so that the seismic fragility of the bridge system has been reduced at different levels of damage.