Abstract: The elastic and elasto-plastic instability behaviors of circular two-hinged steel tube truss-arches were studied by finite element method in this paper. Four types of vertical load are considered in the analysis, namely, full-span and half-span uniformly distributed load, central and quarter concentrated load. The instability mechanism and failure modes of planar and spatial truss-arches were investigated including truss-arch global buckling, local buckling of chords and diagonals, and interactive buckling between them. Besides, the influence of member geo- metric parameters on load-carrying capacity was discussed. This investigation provides an important basis for the establishment of stability design method of steel tube truss-arches in Chinese code for the design of steel structure.