Abstract: Reflective optical systems, with advantages such as large aperture, achromaticity, and lightweight, are widely used in various advanced optoelectronic equipment. However, due to the mismatch of thermal expansion coefficients among the mirrors, structural components, and adhesives, as well as the variation of adhesive layer parameters with temperature, the imaging quality of these systems is highly sensitive to temperature changes. To ensure the stability of image quality over a wide temperature range, it is imperative to establish an accurate digital model of the mirror assembly to guide the optimization of the optomechanical structure and the design of the bonding process. A thermal simulation model of the mirror assembly is established based on thermodynamic equations, and the data interfaces for thermal, structural, and optical analyses are connected. A refined model of the adhesive later is constructed based on Hook's law to correct the mechanical properties of the adhesive layer. Simulation analysis is used to drive experimental design, and the measured results are used to support the precise establishment of the refined model. The results show that the error of the digital model of the mirror assembly is less than 30 nm after correction. The established digital model of the mirror assembly can provide guidance for the design of reflective optomechanical systems and improve the stability of image quality of reflective optical systems over a wide temperature range.