Abstract: To solve the subsequent casing levels limited by surface casing size in the subsea wellhead system for deepwater drilling, a ?406.4 mm oversized liner hanger technology and corresponding cementing process are introduced. The hanger device is composed of carrier bar and supporting hanger. The maximum outside diameter of the ring is 508 mm and the minimum inner diameter is 445.8 mm. It is prefabricated on a ?508 mm casing before delivery from factory; the snap ring of the supporting hanger is seated into the corresponding slot of the ?508 mm casing carrier ring to connect the ?406.4 mm liner string. Some problems that may arise during the operation are analyzed and summarized, and suggestions are provided. This technology is helpful to optimize the wellbore configuration and better address the complex formation. It also provides a good reference for similar wells’ operations in the future.