A hybrid motor driven power steering system for a commercial vehicle may include a MDPS unit to generate motor output torque depending on driver steering torque, an EHPS unit to generate hydraulic output torque considering the motor output torque of the MDPS unit, a ball nut type gear box to generate output torque which operates a tie rod leading to left and right wheels after being input with the driver steering torque, the motor output torque, and the hydraulic output torque, and two torsion bars to block torque fluctuation rates at respective regions of a joint by detecting a road surface reaction force transferred to a steering column through the ball nut type gear box in at least two different positions. Accordingly, it may be possible to provide a steering capacity required in small-sized, medium-sized and full-sized commercial vehicles.
