Abstract. In this paper, the elasto-plastic dynamic analysis on the steel spatial arch truss with 30 m span and 0.1 rise-span ratio is carried out under earthquake wave with SAP2000. In the analyses, the geometric and material nonlinear effects are considered at the same time based on the plastic-hinge theory. Under the action of EL 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 horizontal direction is 517 gal, and is 387 gal when applied in vertical direction; The ratio of its maximal node horizontal displacement and its structural height is 1/96, and its displacement ductility coefficient is 2.636; The ratio of its maximal node vertical displacement and its structural span is 1/589, and its displacement ductility coefficient is 1.08.