Abstract: Yuanba No.1-side1 well is an important a side-tracking exploration well based on Yuanba No.1, which is disposed to reveal the situation of reef beach phase pay zone gas reservoirs in Yuanba area. It is currently the deepest well with the final inclined depth 7427.23 m and the run in hole (RIH) depth of the flush liner ?146.1 mm 7425.81 m in southeastern Sichuan. It features in high temperature and pressure, high drilling fluid density, small annular clearance, inclined well bore, great offset, long open hole, and small clearance. In addition, a lot of technical problems need to be solved. For instance, centralizers can not be added to the flush casing, to keep casing centralized inside the well bore gets difficult, and circulation loss is likely to occur. Systematic cementing methods are adopted, such as the optimization of high temperature resistance cementing slurry system and weighted spacer fluid system, the rational design of RIH string combination, the use of balanced pressure cementing techniques, and the improvement of slurry making method. All the methods ensure the casing is run in hole successfully, solving the problems like circulation loss, poor displacement, high pump pressure, and gas channeling. Cementing operation runs successfully, and logging interpretation shows the cementing quality is excellent. The successful well cementing creates the record of ultra deep well cementing in southeastern Sichuan, providing useful reference for cementing of ultra deep wells and wells of small clearance in the future.