To study evolution of the void in the material of a motor rotor under different working conditions from a mesoscopic perspective, damage analysis of the rotor has been carried out based on thermal-mechanical coupling theory. According to the test methods of GB/T 228.1-2010 Part 1 and GB/T 228.2-2015 Part 2, tensile tests were conducted on rotor ma- terials at different temperatures to obtain basic mechanical property parameters, and pa- rameters of the fine-scale damage model at different temperatures were fitted by combining orthogonal tests and a finite element inverse calibration method. Then, the accurate tem- perature distribution law of the motor rotor was obtained through CFD calculation. Based on the material parameters and temperature data, the void evolution of the rotor material under thermal-mechanical load was studied by using the finite element method. The results show that: under the rated conditions, the stress concentration of the rotor is mainly ap- peared in the joint with the shaft, the maximum stress was 304.1MPa, which did not reach the yield limit of the material. No plastic deformation occurred, so the volume fraction of voids inside the rotor material did not change still for the initial pore volume fraction of 2.5 · 10⁻³. In the peak condition, the stress concentration appeared in the rotor plate across the joint of the magnetic bridge and pole shoe with a maximum stress of 354.4MPa and a small plastic strain of 1.133 ·10⁻³. The pore volume fraction increased to 2.503 ·10⁻³, where the initial pore growth of 2.150 · 10⁻⁶ and the secondary pore nucleation of 2.079 · 10⁻¹².