Abstract: The double-tower central span PC(prestressed concrete)cable-stayed bridge is usually used in economically developed regions with increasing traffic volume and limited condition for setting pier. However, the height-towidth ratio of the main beam of these bridges is quite large, and the research on seismic performance of this kinds of bridges is particularly important. In order to study the influences of the souring effect on seismic responses of this kind of cable-stayed bridge, taking a bridge with 400 m main section as an example, by using software SAP2000, the finite element model of the bridge was established to analyze the seismic response of the foundation of bridge under the condition of considering river water erosion and without considering river water erosion. The result shows that the axial force and shear force of the main tower critical section are almost unaffected by the scouring, but have a certain influence on the bending moment of the section; the effects of the scouring on the seismic response of the top displacement of the tower, the displacement of the main beam end and the relative displacement of the tower and beam ends are small.