The forth bridge of Xiangtan with a main span of 400 m is a long span cable-stayed concrete-filled steel tubular arch bridge.In this paper

a 3-dimensional finite element model for the bridge is established.Based on the model and the dynamical equation of MDOF structural system

model analysis is carried out by use of subspace method.Then the dynamic characteristics of the bridge is obtained and analyzed.In addition

3D seismic response of this bridge is studied by means of seismic response spectrum method and time history method.With more than five selected seismic records

the effects of the main structural form

different seismic waves and several soil sites on seismic response have been discussed.Conclusions can be drawn as follows:1.The lateral stability of long span cable-stayed concrete-filled steel tubular arch bridge is notable.2.The whole aseismic capabilities of the bridge is better than long span concrete-filled-steel-tube（CFST） arch bridge.The internal force of arch is evenly distributed

under plane earthquake input or vertical earthquake input.The internal force of tower is also very small.3.The structural seismic response is influenced greatly by the characteristics of different seismic waves

such as natural vibration period and soil sites.4.The maximum seismic response of long span cable-stayed concrete-filled steel tubular arch bridge appears in arch spring and transition section

which should be considered in bridge design.The results obtained in this paper also provide theoretic basis for seismic design and study of cable-stayed arch bridge.