With the accelerated development of information technologies, digital and intelligent development has gradually become an important means for oil and gas companies to cope with the pressure of carbon emission reduction and large fluctuations in oil prices, maintain competitive advantages, and achieve high-quality development. This paper discusses the trend and great value of digital transformation brought by information technologies to oil and gas companies in China and abroad, summarizes four development stages of international petroleum engineering software, as well as the development and application of integrated E&P platform and real-time drilling operation center, and introduces the top-level design scheme and successful practice of digital transformation of CNOOC. CNOOC has carried out smart oilfield construction by using advanced information technologies, established the network communication systems for offshore platforms and drilling ships, and developed the real-time E&P decision-making system, “Xuanji” rotary steering drilling and logging while drilling system, drilling expert decision-making system (E-Drilling), and integrated design cloud platform for drilling and completion, which have achieved excellent application results. This paper also analyzes four challenges in digital and intelligent development in China’s offshore petroleum engineering and puts forward five suggestions for development.