In deep oil and gas development, it is difficult to drill targeted with traditional sliding drilling tools because of the increasing number of wells with complex structure. To help solve the problem of wellbore trajectory control in complex structural wells, a discontinuous directional rotary steerable structure was proposed. Moreover, a mechanical model of discontinuous directional rotary steerable bottom hole assembly(RSBHA) was established by combining the element division idea of finite element method and the continuous beam-column theory. The bit side force and dip angle of were calculated by compiling mechanics program. The effects of borehole geometry parameters, drilling parameters and drill assembly structure parameters on mechanical properties were analyzed. It is concluded that weight on bit and inclination of hole have little influence on bit side force, but the structural parameters of drill assembly have great influence. The research results provide theoretical premise for the optimization of RSBHA structure and drilling parameters, and provide mechanical support for accurate control of wellbore trajectory.