Theoretical research and earthquake damage investigation have shown that there is un-negligible spatial vibration resulting from coupled translation and torsion responses of structures when earthquake occurs. Main reasons are due to facts that both structures are unsymmetrical and seismic ground motions are of multiple components including rotational components. Sometimes the twist damage of structure is predominant during seismic motion. Thus

it is quite significant to take this coupling effect into account in structural dynamic response analysis. Firstly

spatial mechanical model and dynamic equation of the eccentric structure are established in this paper

and corresponding Matlab programs are compiled to solve the corresponding formulas. And then

the dynamic system represented by the dynamic equation is expressed by the state space method. According to the state equation

an emulative model is built using Simulink in Program Matlab so that the dynamic response can be obtained. The coupled translational and torsional responses of a six story frame structure with bilateral eccentricities under the action of two-way horizontal seismic ground motions are investigated by applying the earthquake records: El Centro

Taft and Seattle waves. The effects of eccentric ratio of structure on the coupled translational and torsional responses of structure subjected to multiple ground motions are discussed and some conclusions with engineering significance are drawn.