Digital oilfield is the main means to increase production and income. Developing ultra-short radius sidetracking horizontal wells in old wells requires high-performance well trajectory control. In this paper, the ultra-short radius flexible drill pipe is designed by bionics principle, and logging tool is designed to monitor borehole trajectory in real time by using gamma ray technology. The combination of the flexible drill pipe and logging tool can realize the remaining oil recovery between dense well patterns. The dense well network determines that the drill pipe has a certain bending angle during drilling, and the remaining oil reservoir can be drilled in the shortest distance. The design of drilling tools for ultra-short radius horizontal wells for 7 “and 9-5/8” old well casings is the basis of this paper, the key is to verify the rationality of the design through experiments. The test research shows that, the strength of flexible drill pipe meets the design requirements and importing the monitoring data of gamma logging tool simulating the drilling process of the experimental well into LANDMARK software to describe the well trajectory, the radius of curvature of the deflecting section is 1.5m-2m, meeting the design expectation.