Abstract: Joint-hinge power BHA is the most advanced new tool used in short-radius horizontal well drilling at present. First established the mechanical model of the joint-hinge power BHA in the two-dimensional casing program recommened the solving method and procedures of the model,analyzed in detail the quantitative influences to the lateral force of the drilling bit caused by some structure parameters, wellbore geometric parameters and drilling technology parameters. This paper provided the mechanical analyzing base for the structure designing of the joint-hinge power BHA and the trail control of the short radius horizontal well.