Abstract: The drilling and completion operations in deepwater oil and gas wells of the “Deep Sea No.1” Phase II project face multiple challenges such as concentrated underwater wellheads, high interference risks, complex deep geological conditions, poor drillability, narrow pressure windows, difficult well control, high-temperature and high-pressure, and difficulties in ensuring long-term production. To this end, technical researches on large-scale operation in centralized underwater wellheads, drilling speed increase in deep water and deep layer, deepwater high-pressure well safety control, and deepwater long-term production guarantee were carried out, and key technologies of drilling and completion in deepwater high-pressure gas fields with safety, speed increase, and long-term production as the core were formed. On-site applications in 12 development wells of the “Deep Sea No.1” Phase II project demonstrate that the drilling speed has been greatly improved, and the operating efficiency has been comprehensively enhanced compared with that in the Phase Ⅰ project. The project duration has been greatly shortened, which strongly supports the smooth production of the deepwater high-pressure gas field of the “Deep Sea No.1” Phase II project. The successful completion of the “Deep Sea No.1” Phase II Project marks a great breakthrough in self-operated deepwater drilling and completion technologies in China and provides technical reference for the development of deepwater high-temperature and high-pressure gas fields in China and abroad.