Abstract: Deepwater and offshore deep formation oil and gas resources are crucial for enhancing reserves and production in China’s offshore oil and gas industry. However, there are multiple challenges for the drilling and completion operations such as complex engineering and geological conditions, extreme environments, high costs, etc. This paper systematically reviews the key technological advancements made by China National Offshore Oil Corporation (CNOOC) in the fields of deepwater and offshore deep formation drilling and completion, and outlines the future development directions. It aims to provide theoretical support and practical references for safe and efficient development under complex scenarios.To address core challenges such as well control overflow monitoring, wellbore integrity, and efficient completion in deepwater complex wells, CNOOC has innovatively developed seabed gas invasion early warning systems, full lifecycle annular pressure management technology, and multi-channel bypass screen equipment, etc. These innovations have successfully ensured the successful commissioning of major projects such as the“Deep Sea No.1”ultra-deepwater gas field. To address the bottlenecks of complex offshore deep formations and high development costs, CNOOC has proposed key technologies such as multi-source information fusion for structural identification, high-temperature-resistant and low-cost corrosion prevention, and open-hole sidetracking in hard formations. These technologies significantly have improved development efficiency in deep gas fields such as BZ19−6. However, technical bottlenecks still exist in complex scenarios such as ultra-shallow gas zone development in deepwater areas and superposition of high temperature and high pressure working conditions in deepwater, while the localization level of critical tools, equipment, and engineering design software requires further enhancement. Future efforts should focus on breakthroughs in intelligent control of ultra-deep drilling, full lifecycle corrosion prevention optimization, and disruptive green technology research and development, so as to strengthen independent control capabilities and promote efficient exploitation of China’s deepwater and offshore deep formation oil and gas resources.