Seismic response of a high-rise building under rare earthquake is numerically investigated in the paper. The Height of the building is 266m, which goes beyond the limit of 150m in Chinese standard, so nonlinear analysis should be performed to investigate its elasto-plastic behaviors under severe earthquake excitations. In the finite-element model for analysis, beam-column members of the structure are simulated by beam elements, while the core tube is simulated by shell elements. The concrete damage plasticity model is used for concrete members, while the kinematic hardening rule is defined for steel beam-column members. Four sets of earthquake wave, including 3 sets of strong earthquake records and 1 set of artificial wave, are adopted in the analysis. The analysis results show that, under severe earthquakes, steel frame members and steel truss members in the strengthened floors keep elastic. Severe damages are detected in almost all coupling beams in the core tube, as well as shear-walls near strengthened stories, where lateral stiffness would decrease seriously. Through the investigation, it is also found that the largest story drift is less than the maximum allowable value in the Chinese code for seismic design of buildings. So it is concluded that the high-rise building will not collapse when the place is subjected to severe earthquakes. Besides, some design suggestions are proposed according to nonlinear dynamic analysis in the paper.