Abstract: It is of great significance to utilize the horizontal well with short radius to enhance the oil recovery in mature regions,reconstruct the old well and reduce the exploration cost.This paper introduces the slim hole sidetracking hori-zontal well drilling technology from the aspects of the con-struction difficulties,profile design,trajectory control,fric-tion calculation,the selection of measuring methods and tools,as well as the design of drilling fluid of ultradeep short-radius horizontal wells.Based on drilling practice,it shows the structure of BHA and technological measures for each drilling stage.The success of TK1105CH has accumu-lated valuable experience for ultra-deep short radius hori zontal well.