Abstract: The extradeep oil reservoir of fault-karst rock mass in the Shunbei Oil and Gas Field is exploited mainly by means of horizontal well. Well Shunbei 5-5H is a slim-hole horizontal well (Ø120.65 mm) in this oil and gas field. It drills into Permian and Silurian where circulation loss is complicated. In addition, the formation temperature is high, orienting tool is insufficient and the friction torque is large. Therefore, it is faced with the difficulties of safe well completion, trajectory control and displacement extension. To deal with the complicated circulation loss in this well, the special-sealing casing program was optimized and the lost circulation techniques were adopted to ensure the safe well completion. Hole trajectory optimization technique, high-temperature measurement tool, friction drag reduction technique, displacement extension evaluation and slim-hole trajectory control technique were researched and developed to form the ultradeep slim-hole (Ø120.65 mm) directional drilling techniques. Based on their integrated application, the drilling construction of Well Shunbei 5-5H is smoothly performed with the total depth of 8 520 m. The research results enrich the directional drilling techniques for ultradeep slim-hole horizontal wells and provide the technical support for the exploration and development of extradeep oil and gas reservoirs in the Shunbei Oil and Gas Field.