The study aims at addressing a critical need in ground-based optoelectronic imaging, which is enhancing the surface form accuracy of primary mirrors under extreme conditions such as large pitch angles and significant temperature variations. This aim is vital as it directly impacts on the quality of optical imaging, an increasingly important factor in various applications ranging from scientific research to defense. Recognizing the limitations of traditional support structures in these challenging environments, a novel monolithic shaft support structure was developed in this paper. This new design was targeted to significantly improve the stability and thermal adaptability of primary mirrors, ensuring their performance in demanding conditions. The study involved rigorous theoretical analysis using Castigliano's second theorem and practical optimization using advanced techniques like the multi-island genetic algorithm. These methods were integral to balancing structural stability with precise surface form accuracy, setting a new benchmark in the field. In essence, this research sought to revolutionize the design and functionality of support structures for medium-caliber primary mirrors in ground-based optoelectronic systems, enhancing their reliability and performance in extreme environments. This advancement was not just an improvement but a necessary step to meet the growing demands for high-quality optical imaging in diverse and challenging conditions. A novel single-core-axis support structure was proposed to enhance the mirror's stability and adaptability to thermal expansion. The study utilized Castigliano's second theorem for an in-depth analysis of the impact of the single-core-axis stress size chain parameters on the mirror surface errors. Further, an integration of Isight platform and a multi-island genetic algorithm was employed for optimizing the structural parameters. This approach allowed for a fine-tuned balance between structural stability and surface accuracy. In this study, the fabricated support structure was integrated into the optical system, achieving a primary mirror surface precision with an RMS of 4.4 nm and a PV of 56.28 nm, primarily affected by manufacturing errors and gravitational load. The mirror was positioned horizontally along the optical axis to induce maximal surface deformation (Fig.12). Surface accuracy assessments at room temperatures of 20 ℃ and 40 ℃ revealed RMS values of 15.81 nm and 19.23 nm, and PV values of 83.17 nm and 91.98 nm, respectively. The 20 ℃ temperature variation introduced a form error RMS of 3.42 nm and a PV of 8.81 nm (Fig.13). Extrapolating from these results, under an extended temperature range (-40 ℃ to +40 ℃), the estimated RMS and PV errors are approximately 10.3 nm and 26.5 nm, respectively, well within acceptable limits for optical imaging systems. These findings, validated through interferometric analysis (Fig.13), demonstrate the design's capability to maintain mirror surface accuracy under varied temperature conditions, confirming its suitability for diverse environmental applications. This research addressed the design of support structures for medium-caliber ground-based optoelectronic imaging equipment in extreme temperature differential environments. The monolithic shaft support structure adopted significantly reduced thermal strain and maintained rigid body displacement within acceptable limits. Key structural parameters were analyzed using Castigliano's second theorem, and a multi-island genetic algorithm was employed for multi-objective optimization of structural components. Simulation and physical experiments validated that the primary mirror's surface form error adhered to optical imaging requirements even under significant temperature variations (ΔT=80 ℃). Notably, the optimization of RMS and PV values improved by 59.99% and 23.2%, respectively, with a 21.96% enhancement in rigid body displacement. Future work will focus on extending the application of the monolithic shaft structure to larger aperture mirrors and broader temperature ranges, further optimizing and validating its optical and structural stability. This study provides essential insights for the development of ground-based optoelectronic imaging systems.