Directive rotary steerable drilling system reprensents the most advanced technology in the world and it has been widely used in the horizontal well and controlled directional well. Firstly it is assumed that 2 decentralized rings could enlarge the deviation angle of bit effectively; then by the establishment of mechanics model of rotation axis, the rotation angle equations and deflection curve equations while n=1 and n=2 were derived respectively for comparison to prove the assumption, that is with 2 decentralized rings, enlargement of bit deviation angle, smaller well trajectory curvature radius and optimized steering performance can be realized; and finally mechanics model of decentralized ring B is optimized under the condition of L3=0