Abstract: In the Yingge Sea, the middle and deep strata are characterized by complex geology, high reservoir pressure and high temperature gradient. And there are vertically multiple pay zones, and well kick and circulation loss occur in the same strata. While the safety of field operation is guaranteed, a section of casing is reserved according to the design to avoid the complex situations which hinder the exploration and development of target layers. Well DF13-1-A is located in the complex strata where well kick and circulation loss coexist, so ?177.8 mm casing has to be run in the hole in advance to isolate the upper complex hole section and ?149.225 mm hole is used in the lower section. Faced with the technical difficulties, e.g. restricted slim hole BHA (bottom hole assembly) and high difficulty of well control reservoir protection, a series of measures are taken, such as BHA optimization, drilling fluid optimization and real-time pressure monitoring. And as a result, the slim hole operation is completed successfully. It provides some technical reference for the HTHP slim hole operation in western South China Sea in the future.