The downhole screw motor is a kind of power tool which 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 pressure difference drive the rotor rotating round the stator, provide torque moment and speed to the drill bit, thus the drilling process is performed. The drill pipe is not rotating during work process, so the advantages are appeared comparing with conventional drilling system. The downhole screw motor is suitable for vertical, directional and horizontal well.