Abstract: The depth of Ordovician oil and gas reservoir in Xinjiang Shaya region is more than 6 900 meters.There are many uncertain factors at such depth,making drilling difficult and highly costly.So the ultra-deep sidetracking medium/short radius horizontal Well TP2CX was drilled after Well TP2.There are many technical difficulties,such as ultra-deep casing sidetracking,poor drillability,high pump pressure in slim hole,difficult transmission of measured signal in deep hole,high formation temperature and the big error in well depth design.In view of these difficulties,the wellbore trajectory design of Well TP2CX was modified,whipstock was used for the casing sidetrack,special MWD and PDM were chosen to adapt the slim hole and high temperature,drilling parameters were optimized,the bits were chosen and drilling string was adjusted to form the drilling technology which is suitable for ultra-deep sidetracking medium/short radius horizontal well.Well-bore trajectory design of Well TP2CX:total depth 7 305.33 m,BUR:78.40°/100m,horizontal displacement 465.85 m.The modified well-bore trajectory design of Well TP2CX: BUR 66.67°/100m; total depth 7 453.00 m,horizontal displacement 565.88 m.The technology used in Well TP2CX was very successful for ultra-deep casing sidetrack,effectively solved the issue of the reservoir depth error,avoided unnecessary tripping because of MWD and motor failure,shortened drilling cycle by 26 days,improved ROP,and reduced drilling cost.