Abstract: Understanding and acquisition of force characteristic on positive displacement drill are essential to correct design and application of steering power drill in horizontal drilling. For two different conditions in directional drilling and steering drilling, this paper discusses drilling tool buckling,twinsting,centrifugal inertia force of rotor,axial force of rotor, bearing load,back off moment at stabilizer, bit speed analysis,borehole enlargement and side force distribution of bit. Corresponding calculation equations and theoretical explanation for some field phenomena are presented.