The diagonal grid system does not have the traditional beams and columns, and only has the double-way crossed diagonal columns, and such columns form the tube body.This system has great lateral rigidity, and transmits force in the way of slant axial force.It can effectively overcome generation of the second order bending moment, make up the defect that the beam and column system cannot sufficiently resist the horizontal load, and the internal layout of the building is freer.The structure can be deemed as the supporting frame and tube system, and is different from the ordinary frame and tube structure.The exterior tube consists of diagonal rods that cross in double-way and encircle the external surface of the building continuously.It can overcome the weakness that additional slant bracing is needed if the traditional vertical column bears excessive force.In this paper, the dynamic elastoplasticity analysis for such structure under rarely-occurring earthquake is conducted using the ABAQUS software.For the diagonal grid system of the core tubes in different sizes, mechanical properties of the system under rarely-occurring earthquake action are analyzed.