Geological conditions in northeast area of Sichuan are complicated, such as poor drillability in terrestrial formation, severe deviation in high angle structural belt. Pressure system and strata lithology in this area is also complicated, which causes many complex cases and accidents like lost circulation and collapse when drilling. Besides these, this area have "high pressure, high production, high sourness"  features. ROP was slow and drilling cycle was long. In order to increase ROP of complicated deepwell in south China, through introducing and developing new technology and new tools, like gas drilling and vertical drilling equipments, combined with existing techniques such as underbalanced drilling, compound drilling, optimum drilling technique system fit for complicated deepwell in northeast area of Sichuan was formed, which improved ROP and wellbore quality of complicated deepwell in south China.