Abstract: In order to solve lost circulation, well kick and even blowout caused by narrow safety density window in the western South China Sea, a great effort has been made in studying technologies of the pressure prediction and monitoring in ultra-HTHP complicated formation, the drilling fluid plugging while drilling, the prediction and monitoring of downhole equivalent circulation density, and the high temperature resistant drilling fluid and utra-HTHP cementing. As an achievement, the narrow safety density ultra-HTHP drilling technology suitable for the western South China Sea has been developed. This technology has been applied in seven ultra-HTHP exploration wells in Ledong area, and the occurrence of downhole problems has been significantly reduced. Compared with the same type of wells prior to applying this technology, the average drilling time efficiency increased by 21% and the drilling success rate reached 100%. This showed that the ultra-HTHP narrow density window drilling technology could solve the problems caused by the narrow safety density window in the western South China Sea, and provide technical support for the exploration and development of high temperature high pressure deep water reservoirs.