Abstract: The drilling fluid in ultra-large boreholes has a low return velocity and a weak cuttings-carrying capacity, resulting in serious repeated crushing. Conventional stabilizers easily block returning cuttings, resulting in poor cuttings flowback and a high potential risk of pipe sticking. To address these problems, an improved anti-balling stabilizer suitable for extra-deep wells was developed through improvement measures such as optimizing the shape and size of the diversion surfaces of conventional stabilizers, adjusting the torsion angle of the spiral blades, and changing the radius of the spiral flow channels, etc. Fluid-solid coupling simulations and laboratory scale tests were conducted based on the discrete phase model (DPM) to study the effects of the inlet and outlet diversion surfaces of the stabilizer, the torsion angle of the spiral blade, and the radius of the spiral flow channel on its cuttings-carrying capacity. The results indicate that for the ϕ444.5 mm borehole, when the optimal torsion angle of the spiral blade of the stabilizer is 90°, highly efficient diversion can be achieved, and the residual concentration of cuttings can be reduced while ensuring a small wall shear stress of the spiral blade; when the optimal spiral flow channel radius of the stabilizer’s spiral blade is 230 mm, the velocity in the outlet section can be increased, and the residual concentration of cuttings can be reduced while ensuring a high velocity of the drilling fluid in the acceleration section of the stabilizer; compared with that of conventional stabilizers, the cuttings reflectivity of the improved stabilizer is reduced by 55.7%, and the maximum increase in the cuttings passing rate is 15.15%. During the drilling of the Well SDCK-1, a 10, 000-meter scientific exploration well in the Sichuan Basin, the improved stabilizer (with a spiral blade torsion angle of 90°) has been applied, which effectively reduces the balling phenomenon. The results provide a reference for the design of drilling stabilizers in extra-deep wells, which helps improve drilling efficiency and reduce sticking risks.