【Objective】 To study the load-bearing capacity of variable span and amplitude steel trestle bridges under multiple loading conditions.【Method】 A steel trestle bridge in the construction of the Xiangtang-Putian left line special bridge on the Xiangtang-Putian connection railway line is taken as the research object. A numerical model was established by using the bridge limited element software Midas civil to carefully study the stress state of each component under five different conditions.【Result】 The results show that the bailey beam has a large safety margin under different conditions; the safety margin factor of the pile top distribution beam is small under condition 1 and 2, reaching only 1.23 and 1.20, and the safety margin factor of its stiffness is 1.20 under condition 5. It is necessary to avoid excessive temporary loads during construction; the positive stress safety margin factor of the steel tube column under condition 5 is only 1.50, and measures should be taken to ensure safety during construction; the design of the triangular area at the corner meets the structural performance requirements. 【Conclusion】 The results may provide some reference for the design of similar trestle bridges.