In order to investigate the joint work pattern of upper steel part and lower supporting concrete part，the example of Ningxia flower art center was adopted to create finite element models for upper steel structure only and steel-concrete structure. And a further analysis for the models was done in terms of statistic analysis、elastic analysis under frequently occurred earthquake and dynamic elastic-plastic time-history analysis under seldom occurred earthquake. Besides, the influence of concrete structure’s elastic-plastic property to the whole structure under seldom occurred earthquake was discussed. The results show that structure response such as displacement and internal force increase considerably under joint work pattern. Moreover，the magnification effect of the lower structure about seismic load can not be ignored when designing and analyzing. And the structure’s seismic response will decline if we take into account the lower concrete's elastoplasticity under seldom occurred earthquake.