Diagrid tube structure system has advantages on constructing high-rise buildings due to its great stiffness, however, its seismic performance analysis are limited. 10 CFST diagrid tube-concrete core tube structures are analyzed by Mode-Pushover method using Perform-3D program. The plasticity developing process and components yield order are summarized. The force distribution between diagrid and core tubes is researched and the force redistribution reason is explained from the change of diagrid tube forces. The structure lateral stiffness degradation is discussed based on the developing process of diagrid and core tubes lateral stiffness. The influences of main lateral stiffness related factors on the structure plasticity developing process, force distribution and stiffness change of the tubes are discussed at last.