Abstract: The two methods, the linear and nonlinear bucking analyses, to determine the critical load of a long-span arch bridge of concrete-filled steel tubes were presented. A 3D FE model of Maocaojie arch bridge in Hunan, as an example, was set up, and its stability was analyzed using finite element program ANSYS. The effects of geometry nonlinearity, material nonlinearity and initial defects of the structure on the stability of this arch bridge were investigated. The results show that large displacement occurs at arch top when loading reaches to the load of stability loss, so the effect of large displacement should be considered in the analysis of stability; and the material nonlinearity and initial defects of the structure make its stability decrease.