Abstract: Well F7H of Dongfang 1-1 Gas Field in western South China Sea is the first domestic offshore HPHT horizontal well. In this well, ?148.6 mm bit is used in ?177.8 mm liner to drill to the target layer, so it is necessary to run ?114.3 mm perforation pipe in ?148.6 mm hole for well completion. Well F7H is characterized by slim hole, complex well trajectory and long horizontal section with maximum hole deviation angle of 95.1°. The target layer is lithologically complex with reservoir temperature about 150 ℃ and reservoir pressure coefficient 1.94. The running of perforation pipe in the hole is faced with large torque and drag, instable borehole wall and high well control risk. To solve these problems, the running friction of pipe string is calculated, the high-temperature lubricating drilling fluid system and the specially structured hanging packer assembly are adopted, and overflow and circulation loss are monitored intently. Ultimately, the perforation pipe running is successfully completed in the slim hole of HPHT horizontal well.