Abstract: The construction of Shantou Bay Subsea Tunnel faces complex extreme working conditions characterized by "large diameter, high water pressure, high-intensity seismic zone, high chloride ion erosion, multiple construction method coordination, and multiple active faults". To address these difficulties, the project has developed a number of key innovative technologies: (1) Establishment of a three-level collaborative detection system of "far-field detection + near-field detection + joint inversion" to achieve refined prediction of adverse geology; (2) Proposal of adaptive design technology for shield machines suitable for composite strata, optimizing the cutterhead, cutters, main drive, and tail seal structure; (3) Development of a "sea surface – tunnel interior" collaborative deep-hole grouting technology for fault fracture zones in the sea area, reducing the impermeability coefficient to 10^-7 cm/s; (4) Formation of an integrated seismic resistance and waterproofing technology for high-intensity seismic zones, improving the seismic isolation effect by 30% and achieving zero leakage at joint waterproofing; (5) Pioneering of a large-span in-situ cavern shield machine dismantling technology under the seabed, increasing dismantling efficiency by 30%; (6) Construction of a BIM-based digital construction platform, improving construction coordination efficiency by 30%. Engineering practice shows that these technologies have effectively ensured the safe breakthrough of the tunnel, and the achievements can provide theoretical support and practical reference for similar challenging subsea tunnel projects.