Alloying is widely acknowledged as an effective strategy for enhancing the performance of UO₂ nuclear fuel. Herein, the thermodynamic stability and kinetic stability of U–Th–O ternary compounds are used to clarify the hidden stable structures. The calculation results of the total and the partial density of states indicated that there is significant orbital hybridization between the added Th and O atoms at −5 eV. Furthermore, the mechanical anisotropy was evaluated by means of the three-dimensional Young's modulus, revealing that the U–Th–O ternary compound exhibits a high degree of isotropy, with the Young's modulus reaching approximately 200 GPa in all three directions. In our upcoming work, our focus will be on studying the changes in properties, such as thermal conductivity of the U–Th–O ternary compound, which may provide a data basis for the application of ternary U–Th–O fuel in reactors.