Abstract: With the spans of spatial steel arch structures in the project becoming larger, the overall instability of structures becomes more and more serious. There are no special design techniques on large-span steel arch structures in current design criteria. In the paper, under the actual engineering background of a 46.5m Long-span Steel arch Structure with Arch, considering the long-span structures, variable cross-section form, the initial geometry defects, loading layout and a variety of load conditions, the single arch and the whole model structure were established by the ANSYS software. Then eigenvalue buckling analysis and geometrically nonlinear analysis were carried out, the buckling mode of the structure is identified and the effect of an initial geometric imperfection was studied. The comparison between the test data and that of a theoretical analysis shows that its calculated results accorde well with those from the test data. The results of calculation indicate that the structure is very sensitive to initial imperfection and the existence of the imperfection leads to a significant reduction in the stability load-carrying capacity. The foundational materials will be provided to guide the design of this type of structural systems and to carry out further investigations.