A three-dimensional heat transfer model is built according to the rotor structure of an asynchronous motor, and three-dimensional temperature fields of the rotor under different working conditions, such as the unloaded, rated loaded and that with broken rotor bars, are studied based on the finite element numerical method and experiments. The feasibility of inspecting the motor faults by infrared thermography is also discussed. The following conclusions can be drawn from the study: the temperature field is uniform in the circumferential direction of the rotor and the temperature changes along the axial direction of the rotor with the maximum temperature appearing at the point near the power-output end; the heat transfer in the axes of the motor is the main means of heat dissipation of the rotor; the loss of bearing has a more sensitive effect on the temperature field of the motor end cover when the motor is unloaded; therefore, under this working condition it is easier to detect the fault of the motor bearing by thermography; no obvious temperature change appears when rotor bars are broken, so this fault is out of the range that can be detected by thermography. This study is helpful for undergraduates to understand the inner temperature distribution of the asynchronous motor, and is also of great importance for engineers in the field of nondestructive inspection of motor faults. (Contains 1 table and 21 figures.)