Abstract: The Well Chuanshen-1 encountered an ultra-high temperature and high pressure (ultra-HTHP) formation in the fourth drilling section. In order to ensure the long-term sealing of setting cement in this section, it is preferable to restrain the strength deterioration of setting cement by increasing the silicon powder dosage and by reasonably matching the particle sizes of silicon powder. In addition, the high-temperature styrene-acrylic latex and the nano-liquid silicon have been selected to improve the anti-gas channeling ability, mechanical properties and stability of cement slurry. For this purpose, a high-density anti-gas channeling cement slurry suitable for ultra-HTHP formation was designed, with a density of 2.05 kg/L and an anti-gas channeling coefficient SPN lower than 0.43. In this case, no gas channeling was observed in gas channeling simulation; the compressive strength of set cement reached 41 MPa at 180 °C for 14 d, and no strength deterioration of cement stone was found; the gas measurement permeability of the set cement was 0.008 1 mD, and the uniaxial elastic modulus of set cement was 7.54 GPa. The high-density anti-gas channeling cement slurry was applied in the fourth drilling section of Well Chuanshen-1, and the cementing measures such as "thoroughly displacement", "stable well killing" and "sealing securely" were adopted, which effectively isolated the high-pressure gas layers and provided a good wellbore environment for the successive operations. This process proved that the  ultra-high temperature and high pressure formation could be smoothly cemented by using the suitable cement slurry and taking proper technical measures, and an in following those procedures, it could be possible in the future to assure high cementing quality.