Partition walls are widely used in engineering structures, and their thermomechanical performance has a significant influence on overall safety and durability. Under extreme conditions, such as high temperatures, these walls are subjected to complex thermal expansion, stress development, and deformation, which may compromise structural stability. Analyzing full-field deformation of parathion walls with high accuracy is a burden for classical fine-scale finite element methods. To address these challenges, this study applies a multiscale finite element method to investigate the coupled thermomechanical behavior of partition walls, providing a more computationally efficient alternative to conventional single-scale models. The method effectively captures thermal–mechanical interactions in walls composed of solid steel, porous steel, and composite plates. Numerical simulations confirm the accuracy and efficiency of the proposed approach, demonstrating its suitability for practical engineering applications. The results offer a reliable basis for optimizing partition wall design, improving energy performance, and ensuring structural integrity under demanding operating conditions.