The analysis model under multi?support excitation was established based on the absolute displacement method. The multi?support non?stationary ground motions were artificially synthesized by trigonometric series method.A square and a rectangular multi?support truss models with span of 90 m were selected,and the dynamic response of the two structures under uniform excitation and multi?support excitation were respectively analyzed.Base isolations were adopted at the bottom of the two models,and the differences of structures′ response before and after isolation were investigated through time history analysis.Results showed that the axial forces of control bars vary little under uniform excitation while they change largely under multi?support excitation, under the horizontal earthquake action. The maximum accelerations of truss nodes of the square structure increase under multi?support excitation, but the rectangular structure was opposite.It means the internal forces results were unreliable if uniform excitation was directly used in long?span strictures. The responses of the isolated structures were greatly reduced compared with non?isolated ones, and the regularities were almost consistent under multi?support excitation or uniform excitation.Under the vertical earthquake action,axial forces and the moments of the non?isolated square structure increased a little under multi?support excitation compared to uniform excitation,but the rectangular structure increased more.The axial forces of isolated structures raise instead under uniform excitation. Therefore,the spatial effect of seismic action should be more considered when structures used the vertical seismic action.