In order to accurately obtain the temperature field of permanent magnet synchronous motor， we propose a field-circuit coupling method. This study takes a permanent magnet synchronous motor as the research object， uses MATLAB/Simulink to build the control strategy of the motor， and then deploys the finite element analysis software ANSYS Maxwell and ANSYS Simplorer to build the two-dimensional electromagnetic field model and control circuit model of the motor to form the field-circuit coupling model. The field-circuit coupling model calculates the loss of the motor， and imports the loss into the three-dimensional magneto-thermal coupling model of the motor. Thus， the change of the temperature field of the motor can be observed in the base speed and weak field. The prototype test verifies the accuracy of the method. This method provides a basis for accurate calculation of the temperature field for motors.