Abstract: A 3D fine finite element model of Shanghai Center Tower is established and used to analyze the seismic responses of the structure by applying the modal superposition method in time domain. According to the soil site condition in Shanghai region, seven seismic waves are selected as horizontal inputs. The influence of high-order modes on the seismic responses of the structure is studied, based on the comparison among the numerical results of the seismic responses, obtained from superposition calculations with different number of the structural modes. The result show that the influence to the structural maximum horizontal displacement and maximum angle of relative storey displacement is not obvious, but the influence to the internal force of the structure cannot be ignored. This research provides the reference for choosing the reasonable modal number in superposition calculation of the super high-rise building seismic design.