Abstract: With the horizontal well technology adopted as one of main technologies used for economic-scale development of Sulige Gasfield, the trend to maximizing the production output per well by further increasing the operation length of horizontal section has become more and more imminent. Aiming at the drilling difficulties in ultra-long horizontal section of Well Su 77-21-40H2 in Sulige Gasfield (namely difficult transmission of drilling pressure, difficult cleaning of wellbore, poor wellbore stability and difficult lowering of large-size fracturing tool in completion operation), by taking several technical countermeasures such as optimizing the wellbore profile, introducing the new-type friction resistance reducing tools, optimizing the drilling tool combination and MEG polysulfonate drilling fluid system, installing the top drive equipment, ensuring the smooth lowering of fracturing tool and strictly implementing the supporting measures, the extension length and mechanical drilling speed of the horizontal section of such well have been greatly improved. When the drilling of this well was smoothly completed, the actual length of horizontal section was 2 303 m, which has provided the experience for further development of horizontal wells in Sulige Gasfield.