Concrete casting into the irregular, confined spaces of steel-shell structures presents challenges such as restricted construction access, low temperatures, and insufficient compactness. To ensure the construction quality and long-term performance of steel-concrete composite structures in shield docking sections under low-temperature conditions, a low-temperature-resistant, non-shrinking self-compacting concrete (SCC) is developed based on a case study of the Jiangyin-Jingjiang Yangtze River Tunnel Project. The concrete casting technology within the steel is also optimized. First, the SCC was formulated through systematic mix proportion design and optimization to meet requirements for workability, low-temperature resistance, and volume stability simultaneously. Next, full-scale and scaled-down model tests were conducted to characterize the material properties and validate the casting technology. These tests confirmed the applicability of the developed SCC and its corresponding construction scheme. The results reveal the following: (1) The developed concrete demonstrates excellent workability and mechanical properties at low temperatures. (2) When combined with the optimized construction technology, the concrete’s compactness and filling integrity are significantly improved, fully meeting critical engineering quality specifications. The synergistic innovations in material design and casting processes satisfy stringent engineering quality control criteria, providing a reliable technical solution for concrete placement in confined, low-temperature tunnel engineering scenarios.