Abstract: Fine controlled pressure drilling technology is a new technology developed in recent years, which is mainly used in the safe drilling of the formation with narrow safe density windows and uncertain pressure systems. Based on the development of controlled pressure drilling technology at home and abroad, fine controlled pressure drilling system with domestic independent intellectual property rights is developed to realize the closed-loop fine control of wellbore pressure. At present, the system has successfully implemented controlled pressure drilling operations in 12 wells on offshore platforms (surface wellheads) to ensure the safety of drilling operation. Among them, Well A has achieved safe drilling under the condition of high leakage rate. It shows that controlled pressure drilling can also be carried out under certain leakage rate. Now, take Well A as an example to summarize, in order to provide a reference for similar operations in the future.