Abstract: Irregular windows, low ROP, wellbore instability, large drag and torque make it difficult to ensure the cementing quality in the windowing/sidetracking of slim hole wells in the Subei Basin. Therefore studies were carried out including windowing schemes and tools, wellbore trajectory adjustment and control, special bit design, drilling fluid system selection and cementing technology optimization. According to the different sidetracking points, the proper windowing tools and wellbore trajectory design scheme were optimized, and adopted the spiral sand removal drill pipe to reduce the drag and torque. For the lithological characteristics and different working conditions of the Subei Basin, two kinds of PDC bits were selected, which achieve high single bit footage and increase the ROP. Further, the amine polymer drilling fluid system was optimized, and combined with a high-efficiency extreme pressure friction reducing agent, it can meet the requirements of wellbore stability, cuttings carrying, lubrication and collapse prevention. By adopting the anti-channeling and toughening cement slurry system, combined with the small-sized hydraulic variable diameter casing centralizer and water-swelling packer, the cementing quality can be improved. The above-mentioned key technologies developed in this study have been successfully applied in 9 slim hole in Subei Basin, the ROP was increased by 125.3%, the drilling cycle shortened by 45.8%, and the complex time efficiency reduced by 87.0%, compared with the previously completed wells. Research results showed that the application of those key technologies could effectively improve the ROP, shorten the drilling cycle and reduce the complex time efficiency of slim hole in the Subei Basin, with excellent rapid drilling effect and remarkable promotion value, making it a good potential candidate for adoption.