Abstract: Temperature variations can introduce thermal aberration into optical systems, leading to a decline in imaging quality. This paper takes a certain infrared lens as the research object and obtains the imaging quality at the best image plane under －40℃ to 60℃ temperature conditions using optical thermal analysis and opto-mechanical-thermal integrated analysis. The results of the thermal analysis indicate that there is no significant degradation in the imaging quality of the optical system under both high and low temperature conditions.; while the results of the integrated analysis show that at －40℃, the system exhibits significant spherical aberration. The difference in the surface form between the two methods makes the defocusing amount results obtained from the integrated analysis generally larger than those from the thermal analysis. Finally, through surface form tolerance analysis, it was determined that the thermal deformation distortion of Lens 1 is the primary source of spherical aberration, while the thermal deformation distortion of lens 2 is a key factor contributing to defocusing discrepancies. This was further verified during the surface optimization process.