<p>Ta/Re-laminated composite materials show promising application prospects in space engine nozzles. The physical and chemical properties of the Ta-Re solid solution at the Ta/Re interface are crucial determinants of the composite’s high-temperature performance. This study explores the stability, mechanical, and thermodynamic properties of the ReTa₃ solid solution using first-principles calculations. The formation enthalpy (<i>ΔH</i>) and cohesive energy (<i>E</i>_<i>coh</i>) of ReTa₃ are calculated to be − 0.171&#xa0;eV/atom and − 9.805&#xa0;eV/atom, respectively. These data indicate that ReTa₃ can form spontaneously and is energetically stable. The solid solution exhibits notable mechanical properties, including high toughness (Pugh’s ratio = 3.70) and hardness (H_V = 3.86 GPa), along with low anisotropy. Thermodynamically, at 0 GPa and 2000&#xa0;K, the average atomic heat capacity of ReTa₃ (<i>C</i>_p = 27.485&#xa0;J·mol⁻¹·K⁻¹) closely matches that of Re (<i>C</i>_p = 27.183&#xa0;J·mol⁻¹·K⁻¹) and Ta (<i>C</i>_p = 27.576&#xa0;J·mol⁻¹·K⁻¹). The coefficient of thermal expansion for ReTa₃ (<i>α</i> = 2.459 × 10⁻⁵·K⁻¹) lies between those of Re (<i>α</i> = 2.011 × 10⁻⁵·K⁻¹) and Ta (α = 2.648 × 10⁻⁵·K⁻¹) at 0 GPa and 2000&#xa0;K. Such a property effectively reduces the temperature gradient within the material, thereby mitigating the risk of thermal cracking and interfacial debonding. These behaviors are attributed to the hybridization of electron orbitals between Re and Ta atoms, leading to energy level splitting at the Fermi level and a reduction in the bond energy of pseudo-covalent bonds within the unit cell. This comprehensive analysis of ReTa₃ provides insights into the electron transfer mechanisms that govern its properties and offers a theoretical foundation for the composition control and performance optimization of transition layers in Ta-Re-layered composite materials.</p>