Abstract: Well A1H in the Enping 21–4 Oilfield in the eastern South China Sea is an ultra-deep extended reach well. ϕ244.5 mm casing can reach a depth of 8 125.00 m, with an open hole length of 5 125.00 m and a horizontal displacement of 5 093.17 m in the open hole section, suggesting challenging casing running. Three faults were encountered during actual drilling, which heightened risks of cementing loss and compromised cement quality assurance. In order to overcome the technical problems for cementing in Well A1H, the wear evaluation device of casing accessories was developed, and the evaluation and optimization of drilling accessories were completed, which provided technical support for safe and smooth casing running. The precise calculation technology of circulating friction was used to realize the accurate control of wellbore pressure and the optimal design of the slurry column structure during the operation, effectively reducing the risk of cementing loss. A dual-suspended ultra-low-density and low-friction lead slurry and a high-solid content, low-viscosity, and high-cut tail slurry were employed to ensure that the fluid rheology in the well was properly matched, improving cementing displacement efficiency. Temperature-pressure coupled calculation accurately evaluated bottomhole circulating temperature, offering rational temperature parameters for cement slurry tests. Through the integrated application of these key cementing technologies, the Well A1H in the Enping 21–4 Oilfield achieved smooth cementing operations. This case provides technical support for cementing ultra-deep extended reach wells in the sea area.