Research conclusions:Through establishing the dynamic analysis mechanic model for twin towers single cable –stayed bridge, the dynamic characteristics and temporal process of earthquake are analyzed for twin towers single cable –stayed bridge with finite element method. The modal analysis shows the first modal of twin towers single cable -stayed bridge is the vertical symmetrical bend ofmain beam, with bigger self -vibration frequency than the floating cable –stayed bridge, so the twin towers single cable -stayed bridge ismuch influenced by vertical earthquake, wind and vehicle vibration. The internal force and deformation law of the structure of the bridges encountered many earthquakes are studied, and the seismic performance of the cable -stayed bridge is analyzed. The study shows some cable –stayed bridge canmeet the seismic requirement stipulated in the design code under effect of encount eringmany earthquakes with the transcendental possibility of 10% in 50 years.