Low speed high torque direct drive motor has been widely applied in various industries. However, operation faults occur frequently due to the complex working conditions of the motor, especially the locked-rotor fault. Therefore, it is necessary to do deeply research in this case of the electromagnetic field and the temperature field distribution of the motor. Taking a 5kW, 10-pole tangential type Low speed high torque permanent magnet (PM) motor for example, based on field-circuit coupled finite element method, 2-D motor field, circuit and motion coupling is achieved. On this basis, the temperature field of the motor is analyzed. Finally the results which are consistent with the actual project are obtained.