With the increasing urbanization in China, the scale of urban elevated bridge construction continues to expand. Conventional ground-supported formwork systems face significant challenges in the construction of high-pier, large-span prestressed bent caps. These traditional systems, characterized by large site occupancy and high material consumption, often lead to low construction efficiency. Particularly in space-constrained urban centers, their bulky support structures severely disrupt surrounding traffic and fail to meet urban bridge construction demands. In this paper, a lightweight, ground-free formwork support system for high-pier bent caps is systematically investigated. By employing novel materials and structural forms, such as acrylonitrile-styrene-acrylate (ASA) polymer-reinforced alloy formwork and ground-free steel supports, the system achieves lightweight, modular, and green construction. It innovatively addresses multiple technical difficulties inherent in traditional methods, significantly reduces carbon emissions during construction, improves material reusability, and embodies the concept of sustainable construction. Engineering practices in typical projects, including Wenzhou Wenrui Avenue, Hangzhou Shidai Avenue, and Ningbo Jiulong Avenue, have demonstrated the marked effectiveness of this system. It has significant advantages in terms of construction efficiency, cost control, resource conservation, and environmental impact, indicating substantial potential for broader application.