Abstract: Yuanba Gas Field is the deepest large bioherm marine gas field in China, which is characterized by ultra depth, high temperature, high pressure and high sulfur content, and its main development target layer is the Permian Changxing Formation. In recent years, some wells have drilled into the deeper strata as the exploration continues. For example, Well Chuanshen 1 drills into Dengying Formation and its total depth is up to 8 420 m. And its casing program is complex with multiple casing levels. In order to solve the technical difficulties in the last small-liner cementing, such as slim hole, narrow clearance and “one ultra and three highs” (ultra depth, high temperature, high pressure and high sulfur content), this paper studied the small-liner cementing technology for ultra deep exploration wells of Yuanba Gas Field. High-temperature latex and nanometer silicon emulsion were selected as the anti-gas channeling agent, the supporting corrosion inhibitor was prepared, and high-density slurry was designed according to particle-size distribution principle. In addition, the high-temperature set cement strength degradation prevention technology and the acidic gas corrosion inhibition technology were established, and the enhanced high-temperature, anti-gas channeling and anti-corrosion slurry system was developed, whose adaptive temperature is as high as 180 ℃, density is 1.88-2.25 g/cm³ and SPN is less than 1. After the set cement is kept under 180 ℃ for 48 h, its compressive strength is higher than 14 MPa and its elastic modulus is lower than 8 GPa. What’s more, its long term strength doesn’t degrade. And it is resistant to the corrosion of H₂S and CO₂. It is applied to Ø139.7 mm ultra deep small-liner cementing in Well Yuanba 7-C1 and Well Chuanshen 1 and their high-quality cementing ratio is 100%. It is also applied to Ø193.7 mm production-casing (liner) cementing in Well Yuanba 204-1H, Well Hejia 202H and Well Chuanshen 1, and their comprehensive high-quality cementing ratio is 67%. Research and application results show that the high-temperature, high-pressure, anti-gas channeling and anti-corrosion cementing technology can effectively solve the cementing difficulties of ultra deep exploration wells in Yuanba area and similar sour gas fields.