Abstract: In the drilling process of the upper ultra-large borehole of 10 000-meter deep well SDCK1, there are five major technical challenges such as high safety risk of drilling tool, low cleaning efficiency of borehole, difficult quality control of wellbore, fast wear of polycrystalline diamond compact (PDC) bit, and hard ultra-large casing running. To address these challenges, the research on drilling tool safety guarantee technology, optimization of ultra-large borehole cleaning, development of High flow rate and erosion-resistance inclinometer, selection of “personalized PDC bit + high-torque hollow screw”, and optimization of ultra-large and overweight casing running was carried out, and the safe and efficient key drilling technologies of the ultra-large borehole of 10 000-meter deep well were formed. The technologies were applied in the ultra-large borehole of ϕ812.8 mm and ϕ593.7 mm of Well SDCK1 during drilling, which effectively ensured the safety of the drilling tool, borehole cleaning, and quality control of the wellbore (deviation angle is no more than 1°). In addition, single footage and rate of penetration (ROP) were effectively raised, and the ultra-large and overweight casing running to the designed position was smooth. The successful completion of the ultra-large borehole of Well SDCK1 provides a successful experience for the safe and efficient drilling of ultra-large boreholes in the Sichuan area.