Arch bridges are well-suited to mountainous regions because their force characteristics align with local site conditions. However, construction in such areas faces challenges including large temperature differentials, complex canyon wind fields, and rugged terrain. Arch-forming also entails extensive work at height, high construction risk, and difficulties in achieving precise alignment after forming. To overcome these issues, this study presents an intelligent arch-forming method for large-span arch bridges. First, an optimization model for the entire arch-forming process is established to compute cable forces that meet objectives during construction. Second, a digital preassembly-based manufacturing control scheme is developed, allowing high-precision virtual assembly of arch rib segments in a digital environment. Finally, an automatic installation attitude adjustment strategy is proposed, based on restoring the structure to its designed shape, enabling high-precision, automated adjustment of the three-dimensional installation attitude of arch rib segments. The proposed method has been successfully applied to the Deyu Expressway Wujiang Bridge (with a main span of 504 m) located in Guizhou Province, China, demonstrating its reliability and practicality. This approach offers guidance for low-labor, resource-efficient, rapid, and automated construction of large-span arch bridges.