With the acceleration of urbanization, the amount of construction solid waste has increased dramatically. How to effectively deal with and utilize these wastes has become a major challenge in environmental management and resource recycling. Transforming these wastes into recycled concrete is a feasible way to solve this problem, where the thermal stability of concrete is a key attribute to ensure its structural safety. This study, based on thermodynamic principles, delves into the thermal stability of building solid waste recycled concrete. Firstly, the multiphase heat conduction behavior of recycled concrete is analyzed, and a thermodynamic model is used to simulate the heat exchange process between different phases; secondly, through the grey relational analysis method, the thermal stability performance of recycled concrete under different conditions is comprehensively evaluated. Previous studies mostly relied on simplified physical models or empirical formulas to predict the thermal stability of recycled concrete, which cannot fully reflect the impact of the material's microstructure and complexity on its thermal behavior. To overcome these shortcomings, this study proposes a new method combining multiphase heat conduction analysis with grey relational evaluation, aiming to provide a more accurate and practical model for predicting thermal stability. The research results verify that the proposed method can effectively reveal the contribution of each constituent phase to the thermal stability in recycled concrete, which is of great significance for the realization of high-performance, sustainable recycled concrete material design.