Flexible drill pipe is an important part of drilling tools for ultra-short radius horizontal wells, and its structural design directly affects the working performance of drilling tools. According to the strength condition of the flexible drill pipe and the geometric relationship with the guide screen, the structural parameters of the flexible drill pipe satisfying different radii of curvature of the wellbore were obtained; the non-linear contact between the ball head column key and the groove and the material difference of the flexible drill pipe were considered, a single-section flexible drill pipe finite element model was established by using the finite element method; simulation analysis of flexible drill pipes with different structural parameters was carried out. They all meet the requirements of strength and rigidity, verifying the rationality of the parameterized design of flexible drill pipes. The research results can provide a theoretical reference for the structural design of flexible drilling tools for ultra-short-radius horizontal wells.