Abstract: The geometric structure, electronic structure and mechanical and thermal properties of (La_1−xGd_x)₂Ce₂O₇ (x was mole fraction with values of 0, 0.25, 0.50, 0.75 and 1.00) were studied with different Gd doping amounts by first-principles calculation based on density functional theory. The results show that the band structure of (La_1−xGd_x)₂Ce₂O₇ was Γ-X indirect band gap, and the band gap decreased with the increase of x. With the increase of x, the lattice constant and volume of (La_1−xGd_x)₂Ce₂O₇ first decreased and then increased, the relative molecular mass increased, and the density first increased and then decreased. The mechanical properties of (La_1−xGd_x)₂Ce₂O₇ all agreed with the Born-Huang stability criterion, indicating that (La_1−xGd_x)₂Ce₂O₇ had good mechanical stability. The Pugh´s ratio (ratio of shear modulus to bulk modulus) was less than 0.571, and the Poisson's ratio was greater than 0.26, indicating that (La_1−xGd_x)₂Ce₂O₇ had good toughness and could withstand thermal cycling stress. The minimum thermal conductivity of (La_1−xGd_x)₂Ce₂O₇ ranged from 0.98 W · m⁻¹ · K⁻¹ to 1.26 W · m⁻¹ · K⁻¹, which was lower than that of yttria-stabilized zirconia, indicating that (La_1−xGd_x)₂Ce₂O₇ had good thermal properties and could be used as a candidate material for thermal barrier coatings.