Abstract: Technical difficulties such as low ROP, long drilling cycle, poor cementing quality, and high drilling safety risk occur when drilling the upper part of complex ultra-deep wells in the Bozi 1 Block of the Kelasu structure. To break down these problems, a casing program was optimized in terms of regional geological characteristics and theoretical analysis; a series of technologies in ROP enhencment were optimized; combined evaporite bed determine technology was proposed, and a series of antileaking and lost circulation control technical measures and cementing measures were formulated. Consequently, key technologies for drilling and completion of complex ultra-deep wells in Bozi 1 Block of Kelasu structure were formed. The technologies had been tested in four wells including B1103 with an excellent potential for universal applicability. Compared with the neighboring wells using other drilling and completion technologies, there were many positive advances. For example, the ROP was increased by 34.4%, drilling cycle was reduced by 131 days, and completion cycle was cut by 141 days. This showed that the technologies could solve the technical difficulties in drilling and completion of ultra-deep wells reservoirs in the Bozi 1 Block, ensuring safe and efficient drilling and completion. Hence, the key technologies could be widely adopted in this block.