Abstract. In this paper, the elasto-plastic dynamic analysis on the steel spatial arch truss with 90m span and 0.1rise-span ratio is carried out under earthquake wave with SAP2000. In the analyses, the geometric and material nonlinear effects are considered simultaneously based on the plastic-hinge theory. Under the action of EL-centro wave with the peak increasing gradually, its elasto-plastic dynamic responses have been obtained. The results show that its failure mode under the earthquake action is elasto-plastic dynamic buckling; that its critical peak acceleration of EL earthquake wave when applied in X direction is 635gal, and is 465gal when applied in Z direction; The ratio of its maximal node horizontal displacement and its rise height is 1/486, and its displacement ductility coefficient is 1.029 and the ratio of its bars with plastic hinge appearing when buckling is 0.7% when EL-Centro waves applied on structure in X direction; The ratio of its maximal node vertical and its structural span is 1/604, and its displacement ductility coefficient is 1.022 and the ratio of its bars with plastic hinge appearing when buckling is 2.8% when EL-Centro waves applied in Z direction.