Traditional bamboo structures face limitations in strength, joint stability, and fire resistance, making them unsuitable for large-span spatial buildings. This study, based on the Fengshou Theater project in Anjiang Town, Hongjiang City, Hu'nan Province, investigates on-site assembly technologies for free-form double-curved steel-bamboo hybrid roofs, aiming to overcome bamboo's application barriers in modern long-span spatial structures. The research employs a steel-bamboo composite structural system, utilizing steel frameworks for primary support combined with cable-supported bamboo beams and edge arches to achieve rigid-flexible collaborative load-bearing. Material durability issues are addressed through rigorous selection and multi-layer protective treatments, while innovative solutions like embedded stainless steel sleeves, fine-thread bolts, and cast steel connectors resolve traditional bamboo joint slippage and stress concentration. The construction integrates modular prefabrication with on-site assembly, supported by measurement-calibration technologies to ensure precision installation of large-span curved components. Engineering practice demonstrates that this composite system effectively resolves technical challenges in span capacity, durability, and joint reliability, establishing a comprehensive technical framework encompassing material pretreatment, joint design, and prefabricated construction. It achieves 30% reduction in lifecycle carbon emissions and provides a low-carbon construction paradigm for synergistic development of bamboo and steel structures.