PDM Drill is a type of positive displacement down-hole motor, which can turn the fluid pressure energy into mechanical energy by the drilling fluid. When mud fluid from the mud pump begins flowing into the motor via the by-pass valve, a certain pressure difference is formed at the inlet and outlet of the motor, which drives the rotor to rotate the axis of the stator, and transfers the speed and torque to the drill bit through the cardan shaft and the transmission shaft. Thus, the drilling operation is realized.