Modal analysis is an indispensable part of the research on motor vibration and noise issues. Taking a permanent magnet motor for compressor with a rated power of 1.98 kW as an example, the effects of thermal and interference stresses on the radial natural frequencies of various modes of the motor structure are analyzed. Firstly, the influence of winding and modeling on the modal analysis of motor structure is analyzed. Then, the selection range of motor interference fit is analyzed theoretically, the thermal deformation size of the iron core and casing during the highest temperature rise of the compressor motor is analyzed through finite element simulation of thermal-structural coupling. Based on the selection range of interference fit, the optimal interference fit is selected from the perspective of vibration and noise suppression. Finally, a compressor pre-stressed modal simulation model is established, and the effects of thermal stress and interference stress on the modal natural frequency of the compressor are analyzed. Considering the effects of thermal stresses and interference stresses, the modal of the entire machine can be calculated effectively and accurately, which improves the accuracy of the NVH performance assessment of air-conditioning compressors.