Thermal imaging systems, operating in harsh environments and generating substantial internal heat, are prone to thermal axis deviations, posing a severe threat to their targeting performance. Consequently, the simulation analysis and optimization design of the thermal axis stability for military thermal imaging systems are of paramount importance. This work aims to address these issues and enhance the thermal axis stability of military thermal imaging systems through simulation analysis and optimization design, ensuring accurate targeting performance in adverse operational conditions. In order to enhance the thermal axis stability of the infrared thermal imaging system, this study primarily focuses on a key sensitive component of the system, the optical path folding reflector assembly. The research investigates the variations in the thermal axis under different environmental temperatures. To achieve this, a finite element simulation model for the optical path folding reflector assembly is constructed (Fig.1), and a testing system is established (Fig.5). The simulation model demonstrates a high level of consistency with experimental data. Based on this, a topological optimization simulation technique, utilizing a variable density approach, is employed (Fig.3). The primary design objective is to maximize stiffness, while adhering to volume fraction constraints (Fig.4). Through experimental test, it was determined that the optimized design of the folding mirror mount resulted in significant improvements in thermal stability. The high-temperature axial displacement was reduced from 46.1" to 25.5", marking a substantial decrease of 44.7% . Likewise, the low-temperature axial displacement decreased from 92.9" to 51.0", indicating a notable reduction of 45.1% (Fig.6). These outcomes underscore the substantial enhancement achieved in the thermal stability of the folding mirror. Subsequently, the optimized folding mirror was integrated into a specific thermal imaging system for comprehensive system-level test. The testing results confirmed the tangible benefits of the optimization approach. Specifically, the high-temperature axial displacement of the complete imaging system decreased from 0.461 mrad to 0.340 mrad, marking a significant reduction of 26.2%. Furthermore, the low-temperature axial displacement was reduced from 0.485 mrad to 0.296 mrad, representing a substantial improvement of 39.0% (Fig.7). These practical validations affirm the feasibility and effectiveness of the simulation and topological optimization models. In conclusion, this research demonstrates the viability and efficacy of employing simulation and topological optimization techniques, significantly improving the thermal stability of the folding mirror in military infrared imaging systems. The achievements offer a robust foundation for subsequent efforts in lightweight system design and performance enhancements in military infrared thermal imaging systems. This study, based on a structural thermodynamics simulation model, has significantly improved the consistency between simulation and experimental results for the folding mirror under different temperature conditions. Employing a topological optimization method based on variable density, structural optimization was conducted for the thermal imaging system's folding mirror component. The primary optimization objective was to maximize structural stiffness, which led to the determination of the optimal material distribution within the folding mirror. Firstly, the simulation data of the folding mirror's optical axis thermal displacement before and after optimization was compared, it is evident that the high-temperature axial displacement of the folding mirror decreased from 44.5″ to 17.7″, resulting in a substantial reduction of 60.2%. Similarly, the low-temperature axial displacement of the folding mirror mount decreased from 87.8″ to 43.0″, marking a significant reduction of 51.0%. Secondly, by comparing the experimental test data of the folding mirror's optical axis thermal displacement before and after optimization, it is evident that the high-temperature axial displacement of the folding mirror decreased from 46.1″ to 25.5″, resulting in a substantial reduction of 44.7%. Similarly, the low-temperature axial displacement decreased from 92.9″ to 51.0″, marking a significant reduction of 45.1%. Finally, the experimental test data of the high-temperature axial displacement of the complete infrared thermal imaging system before and after the installation of the optimized folding mirror was compared, it is observed that the high-temperature axial displacement of the imaging system decreased from 0.461 mrad to 0.340 mrad. This reduction represents a significant decrease of 26.2%. Likewise, the low-temperature axial displacement decreased from 0.485 mrad to 0.296 mrad, indicating a substantial reduction of 39.0%. The research results demonstrate that through the application of topological optimization techniques, it is possible to achieve a localized, optimal redistribution of materials within the target structure without altering the original structural installation conditions. This effectively enhances the thermal axis stability of the target structure. The technology allows for a more rational allocation of materials, laying the foundation for further improvements in the thermal axis stability of thermal imaging systems and the lightweight design of the complete imaging system.