The downhole screw motor is a kind of power tool that transforms the pressure of liquid to mechanical energy in the downhole. When the power liquid flows into the screw motor, a pressure difference will be produced between the inlet and outlet of the motor, then the differential pressure drives the rotor rotating round the stator, provide torque moment and speed to the drill bit, thus the drilling process is being performed. The drill pipe is not rotating during work process, so the advantages are obvious if comparing with conventional drilling system. The downhole screw motor is suitable for vertical, directional and horizontal.