CCCC has overcome key challenges in constructing cross-sea bridge-island-tunnel clusters under complex marine environments. These challenges include modern immersed tunnel construction with ultra-large burial depth, ultra-large span, and a 120-year durability requirement; rapid island formation using large-diameter steel cylinders; and centimeter-level precision survey and dredging in deep offshore waters with large waves. These technological breakthroughs have supported mega-scale projects such as the Hong Kong-Zhuhai-Macao Bridge and the Shenzhen-Zhongshan Link, forging a new icon in China's infrastructure sector and leading the global advancement of cross-sea engineering technology.