The high temperature stability and wellbore cleaning problems of oil⁃based drilling fluid have to be solved when it is used to drill extended reach wells in the KQT gas field located in the East China Sea. For this reason, the key additives of oil⁃based drilling fluid including the emulsifier, wetting agent, rheology modifier and organic clay were selected using the interfacial tension test, emulsifying efficiency test, microscope observation, emulsion viscoelasticity and rheological property tests. After that, the oil⁃based drilling fluid for extended reach wells was developed, and the comprehensive properties were tested. The results show that the drilling fluid has good stability after hot rolled at 180 °C. The selected rheology modifier can enhance the structure strength of oil⁃based drilling fluid, and effectively increase the gel strength and low shear rate viscosity, thus increasing the wellbore cleaning effect. Meanwhile, it has good filtration property and contamination resistance property. This drilling fluid has been used in 4 wells in the KQT gas field, and good field application results are obtained.