The off-axis concave mirror assembly of the Starborne Proximity Spectrometer (SPM) is a crucial component that significantly impacts its overall performance. Given the stringent requirements for high performance, a meticulous opto-mechanical optimization design was conducted for both the mirror and its support structure within the spectrometer. This comprehensive design process involved numerous iterations and simulations to ensure that the mirror assembly met all the specified criteria for optical and mechanical performance. Microcrystalline glass was selected as the ideal loading material for the concave mirror body due to its exceptional optical properties and mechanical strength. The distribution of reinforcement bars on the back of the mirror body was determined through a sophisticated variable density topology optimization method. This method incorporated sensitivity analysis of the back bar thickness dimensional variables, along with optimization of the local bar thickness and multiple dimensions. The result was a mirror structure with an impressive light weighting rate of 60%, which not only reduced the overall weight but also maintained excellent structural performance. The optimization design for the concave mirror assembly support structure was equally rigorous. To enhance the performance of the mirror and its support structure, mounting holes were added to the back of the concave mirror assembly. This modification allowed for better integration of the mirror within the spectrometer and improved the overall stability of the assembly. In the optimized design of the support structure, a flexible groove was innovatively introduced near the mounting holes. This flexible groove served to mitigate the adverse effects of thermal load on the mirror surface. The main structural parameters of the flexible groove were optimized in a multi-objective manner using a comprehensive evaluation factor Q. This factor allowed for quantitative evaluation of various optimization schemes, ensuring that the final design was both robust and efficient. As a result, a flexible support structure with outstanding performance under optimal structural parameters was obtained. The optical-mechanical integration analysis of the mirror assembly before and after the optimization process revealed significant improvements. The optimized assembly exhibited superior static mechanical performance and better optical performance under both gravity load conditions and thermal coupling conditions. This improvement was attributed to the refined design of the mirror and its support structure, which effectively minimized distortions and maintained high optical accuracy. To further validate the design, a finite element analysis of the concave reflector assembly was conducted. The results showed that the 1st-order intrinsic frequency of the assembly was 942.2 Hz. This value was verified through a sinusoidal sweep test, which revealed a 1st-order intrinsic frequency of 956.5 Hz, with an analytical error of only 1.5%. This indicated that the structure had excellent dynamic performance, which was crucial for ensuring the stability and reliability of the spectrometer during operation. In contrast, the unoptimized assembly exhibited poor typing accuracy under gravity load and thermal coupling conditions. However, the optimized assembly demonstrated significantly better performance under these conditions, particularly under thermal coupling. In the gravity loading condition, the root mean square and peak-to-valley values were 9.5 nm and 46.7 nm, respectively. Under thermal coupling conditions, these values improved to 8.25 nm and 40.6 nm, respectively. These results demonstrated that the mirrors under both conditions had high accuracy in the surface pattern and met the relevant design requirements. Surface pattern inspections of the mirrors under both conditions further confirmed the reliability of the optimized design. The RMS errors were 6.1% and 6.9%, respectively, which were within the allowable error range. This not only verified the accuracy of the integrated analysis but also demonstrated the robustness of the optimized design. Additionally, the dispersive spots generated by the optimized concave mirror assembly were all located within the Airy spots. This indicated that the optimized design met the requirements for the index of performance, ensuring that the spectrometer could provide highly accurate and reliable data on atmospheric pollutants.