Abstract: The X-braced structure has been widely used in the design of major support structures in large-scale ocean engineering, the collapse deformation of the structure may be caused by the buckling instability of the support rod if it is not designed properly. Under the ultimate load, the buckling instability of X-braced structure is a typical multi-span stability problem of columns in essence, and its ultimate bearing capacity is closely related to the structural composition, geometric parameters and end restraint of the strut. This paper mainly studies the buckling characteristics of X-braced structures with or without out-of-plane support under arbitrary elastic supports, focusing on the influence of end constraints, force forms and out-of-plane bracing stiffness. Firstly, based on the linear elastic theory framework, the equilibrium equation of double span compression bar was established, and the buckling load was calculated by newton iterative algorithm, so as to obtain the numerical solution of effective length factor for continuous asymmetric cross struts in mid-span, and the sensitivity analysis of the end support stiffness and mid-span support stiffness is also carried out. Combined with engineering practice, the key design parameters, such as buckling length coefficient and stiffness, are given.