Abstract: In light of the application of polymethyl methacrylate (PMMA) in architectural engineering, this study examines the impact of temperature and joint configuration on its mechanical properties. Uniaxial tensile tests were designed for PMMA specimens over a temperature range from 20°C to 140°C. An in-depth investigation into the tensile mechanical behavior of structural PMMA under high-temperature conditions was conducted. The results indicate that the tensile strength decreases from 90.1 MPa to below 10 MPa as the temperature rises from 20°C to above the glass transition temperature. Based on experimental data and existing theoretical foundations, a new phenomenological constitutive model is proposed to describe and predict the tensile behavior of PMMA under high-temperature conditions. The establishment of this constitutive relationship not only provides a theoretical basis for the design and application of PMMA materials but also serves as a reference for the study of the mechanical behavior of other thermoplastic polymer materials.