The special-type isolated building defined as asymmetric multi-tower structure with large floor is discussed in this paper.The equation of motion for this structure is derived based on the building seismic analysis model.A real multi-tower isolated building with large floor is chose as an example to show the seismic performance of this type of structure.The influences of mass eccentricity and mass ratio on the period ratio

drift ratio and shear force coefficient of the structure are discussed.The following conclusions are obtained:（1）torsional drift obviously depends on the isolated layer in the asymmetric multi-tower with large floor;（2）comparing with the fixed base structures

this special type isolated building can sharply reduce the torsional response;and（3）the effect of isolation reduce with the increase of mass eccentricity of the tower.It is concluded from the study that the multi-tower base isolated building with large floor should be symmetric and concentric for reducing structural seismic response.