Mud motor is a positive displacement screw-type motor powered by downhole circulating drilling fluid, which consists of core components such as stator, rotor, cardan shaft, bearing assembly and output shaft. When the high-pressure mud enters the motor from the inner pipe of the drilling column, it forms a number of sealed chambers between the rubber of the stator and the steel of the rotor, and with the pressure gradient pushes the rotor to make a circumferential movement relative to the stator, which transforms the hydrodynamic energy of the liquid into the mechanical energy of the rotor and transfers it to the bit through the cardanic shaft and the bearings to realize the rotary rock breaking in the bottom of the well. The mud motor has the advantages of compact structure, high starting torque, low speed and high torque output, low impact on surface drilling tools, etc. It is especially suitable for directional wells, horizontal wells and drilling in complex formations, which can significantly improve the drilling efficiency and reduce the rate of downhole accidents, and it can meet the demands of different deep wells, high temperature or high solids mud conditions by changing the number of rotor stages or using high-temperature wear-resistant rubber stator.