Ferroelastic RETaO4 ceramics are promising thermal barrier coatings (TBCs) because of their attractive thermomechanical properties. The influence of crystal structure distortion degree on thermomechanical properties of RETaO4 is estimated in this work. The relationship between Young's modulus and TECs is determined. The highest TECs (10.7 x 10(-6) K-1, 1200 degrees C) of RETaO4 are detected in ErTaO4 ceramics and are ascribed to its small Young's modulus and low Debye temperature. The intrinsic lattice thermal conductivity (3.94-1.26 W m(-1) K-1, 100-900 degrees C) of RETaO4 deceases with increasing of temperature due to an elimination in thermal radiation effects. The theoretical minimum thermal conductivity (1.00 W m(-1) K-1) of RETaO4 indicates that the experimental value is able to be reduced further. We have delved deeply into the thermomechanical properties of ferroelastic RETaO4 ceramics and have emphasized their high-temperature applications as TBCs.