Abstract: Temperature variations can introduce thermal aberrations into optical systems, leading to a decline in imaging quality. In this study, a certain infrared lens was taken as the research object, and the imaging quality at the best image plane was obtained under -40℃ to 60℃ temperature conditions using optical thermal analysis and opto-mechanical–thermal integrated analysis. The results of the thermal analysis indicated no significant degradation in the imaging quality of the optical system under both high and low temperature conditions, whereas the results of the integrated analysis showed that at -40℃, the system exhibited significant spherical aberration. The difference in the surface form between the two methods caused the defocusing amount results obtained from the integrated analysis to be generally larger than those obtained from the thermal analysis. Finally, through surface form tolerance analysis, the thermal deformation distortion of Lens 1 was determined to be the primary source of spherical aberration, whereas the thermal deformation distortion of Lens 2 was determined to be a key factor contributing to defocusing discrepancies. This was further verified during the surface optimization.