In order to reveal the dynamic characteristics of the uniaxial-eccentricity base-isolated structure and establish corresponding simplified method of theoretical analysis,a 3-story 2-span base-isolated steel frame model is investigated by means of the shaking-table tests under different eccentric conditions. Then,the relationship between the torsional effect of the structure and the eccentric condition is discussed. Meanwhile,at different eccentricities,not only the change laws of the shear force,torque and rotation angle between the structure floors before and after the isolation but also the change laws of the acceleration and displacement of the torsion angle of the isolated layer are analyzed. Moreover,based on the layer element model,the simplified dynamic equation of the eccentric isolated structure is established,and the test model is theoretically analyzed. The experimental and analytical results show that the torsional response of the structure can be significantly reduced by the adjustment of the centre of the stiffness of the isolated layer to the mass centre of the superstructure,and that the proposed simplified dynamic equation is capable of effectively stimulating the lateral-torsional coupling response.