Abstract: Well Tashen 5 was deployed to explore the development characteristics and hydrocarbon contents of the Cambrian Shayilike Formation, Xiaoerbulake Formation and the Sinian Qigebrak Formation. Related data indicates that the ultra-deep Well Tashen 5 have several technical difficulties in drilling, such as lost circulation due to fractures and cavities, well deviation due to large formation inclination, and low rate of penetration (ROP) caused by the highly compacted siliceous dolomite. For the lost circulation problem, temperature resistant plugging materials were selected. The ratio and particle size of the plugging materials were optimized to gradually increase the pressure-bearing capacity of the formations while employing the plugging-while-drilling method and progressive plugging methods. In order to solve the conflict between the wellbore quality control and ROP enhancement, the vertical drilling tools and high-torque positive displacement motor (PDM) were applied for deviation prevention and ROP enhancement. In order to solve the problems of low drillability and high abrasiveness of the dolomite formation, the damping and wear-resistant PDC bit and torsion impactor were selected to match with high-torque PDM with iso-wall thickness for compound drilling. Well Tashen 5 was successfully completed after applying above key drilling technologies and provided technical methods and experiences for subsequent drilling in the Cambrian and Sinian of Tahe Oilfield.