Abstract: The deepwater drilling and completion technology in China is still in its infancy. In response to the national deepwater development strategy, CNOOC actively participates in oil and gas exploration and development in the South China Sea and has completed 9 deepwater gas wells with depths of 1 350-1 500 m in the M gas field of Block M in Pearl River Mouth Basin in the South China Sea. The key well completion technologies such as high precision sanding prediction, deepwater sand prevention design, frac and pack process, and mobile security measures have initially developed. Combined with the practice of deepwater well completion in the South China Sea, the possible risk points and field response technological measures in deepwater completion operation are summarized and reasoned to promote the progress of oil and gas exploration and development projects undertaken by CNOOC. Good economic and social benefits are harvested and the experience provides a reference for subsequent design and operations.