Abstract: In this paper, a new model for the dynamic calculation of base-isolated buildingswas proposed,By assuming the building to be continuouse and its defromations to be shearing form mainly,the buliding could be reduced to a based on an elastic bearing.Using analytic methods,vibration frequencies were obtained, and the free vibration functions were given in the analysis forms. Some dynamic characters of base-isolated buildings were discussed, and the relationships between the designed parameters were given directly.The new model looks better than the rigid model.two particles model and multi-particle methods, and easier to be used by engineers.