As the spherical hinge in the bridge swivel structure bears huge vertical pressure, the material and its structural load-bearing capacity are therefore highly-required. In the latest research, the ultrahigh performance concrete material is applied to the spherical hinge structure and the author of this article has conducted a detailed study on the mechanical properties and failure mechanism of this structure; however, there is still no real bridge application at present. In order to ensure the stability of the structure, based on an actual project, this research proposes a monitoring method for the stability of the UHPC spherical hinge horizontal rotation system, i.e., using theoretical calculations and numerical analysis methods. Besides, the mechanical characteristics of the bridge during the process of rotation are predicted, and the monitoring data of the stress of the UHPC spherical hinge, the bending moment of the pier bottom, as well as the acceleration time history of the cantilever beam end are made a comparison to judge whether the rotating posture of the structure is stable. The results show that UHPC spherical hinge features high strength and will not cause axial damage; also, the horizontal rotation system will not cause the unstability due to wind-induced vibration and structural self-excited vibration. Briefly concluded, the theoretical model is basically consistent with the measured data, i.e., the mechanical properties of the structure can be accurately predicted.