Abstract: Low speed and high torque permanent magnet direct drive motor is widely used in large traction, marine propulsion, belt conveyor and other fields, however, due to its large size, this kind of motor has greater difficulties in processing, transportation, assembly and other links, and when some parts of the motor failure will lead to the whole machine can not operate normally, reliability and fault tolerance performance is low. To solve the above problems, a modular winding design method is proposed to realize the flexible assembly of the motor and improve the fault tolerance and reliability of the motor. Firstly, a kind of high torque density double stator low speed direct drive permanent magnet motor is presented, and its structure characteristics and transmission system are introduced in detail. Then, according to the structural characteristics of the motor, the stator efficient modular design method is proposed and its design principles are summarized. Finally, the output performance of the motor without fault and under fault operation is compared by finite element analysis method, and the validity, feasibility and superiority of the proposed modular design method are verified.