<p>The new-type segmental-assembled steel temporary beam buttress in railway construction was taken as the research object. The bending property of this structure was studied through static loading tests of a scaled-down specimen. A theoretical method was put forward to estimate the ultimate bending moment of the splice section. A full solid-element calculation model was established, and the accuracy of this finite element (FE) model was verified through comparison with test results. The effects of the initial joint gap width on bending performance were also studied. The results indicate that the test specimen did not exhibit local buckling or overall instability, demonstrating good vertical bearing capacity. The two splicing sections were identified as the weak areas, and the main failure modes are the tensile failure in the bolt walls of the bottom plates and the bolt shear failure in the web plates. The theoretical method can accurately estimate the bending moment of the splice section. Owing to synchronous changes in the stress state in the same area of the plates near the bolt holes, the load–displacement curve of the FE model showed a “two steps and final strengthening stage” shape. Although the neglection of construction errors in the FE model caused differences between tested and simulated results, the developed FE model accurately predicted the ultimate bending moment. Reducing the initial joint gap width can not only significantly improve the structural vertical bearing capacity under normal service conditions, but also enhance the ultimate bending moment and ductility of the splicing section.</p>