Given the problems of narrow construction sites, difficult construction organization, and high safety and quality risks faced in the construction of bridges in steep canyon regions of mountainous areas, this paper carried out research on key technologies for bridge construction in mountainous areas based on the Yellow River Three Gorges Bridge of the Jiyuan?Xin’an Expressway. For the excavation of deep and large anchorage foundation pits in mountainous areas, a technical scheme of “loosening controlled blasting combined mainly with mechanical excavation and supplemented by manual excavation” was adopted. As this project is a single-tower single-span ground-anchored rotating-cable suspension bridge, the technologies of cable strand folding and coiling and cable strand pre-bending forming were studied and applied. To address the common problems of erecting super-heavy steel girders in mountainous areas, construction technologies such as single-side site overall assembly and bridge deck section-divided girder storage and transportation were adopted; moreover, a construction process simulation analysis was conducted on the steel girder erection to seek the optimal scheme for main girder erection. The research shows that the technologies investigated in this paper have been implemented and applied, which demonstrates that they are not only advanced and efficient but also significantly reduce construction costs, providing a useful reference for the future construction of bridges in mountainous areas with complex terrains.