Abstract: In this paper,a rectangular unit of steel roof in Zhengzhou International Conference Exhibition Center is taken as example and the response spectrum method and time-history method are respectively adopted to explore seismic performances. Geometry nonlinearity and pre-tensions are included in analysis,and the damping ratio and contribution of the former fifty modes are considered. The dynamic actions under horizontal earthquake and vertical earthquake are analyzed. The results indicate that 1) the vertical earthquake action must be taken into account during the process of seismic design; 2) the rules of earthquake action can be gained by means of response spectrum method; 3) it is necessary to carry the time-history analysis for big-span structures; 4) the masts are primary structural load-bearing members,The above analysis can provide a basis of further design and research for this new type of structures.