The mechanical and thermodynamic properties of tetragonal (alpha-) and cubic (beta-) phase Na3PS4 are systematically predicted using the first principles calculations. Our results reveal that both of them are mechanically stable, possess ductile character and the bonding is predominantly of ionic. The predicted H-v shows that both of them are soft material (the H-v of alpha-Na3PS4 is 2.62 GPa and beta-Na3PS4 is 2.15 GPa). Both of them have anisotropic features, and the anisotropic of alpha-Na3PS4 is smaller than that of beta-Na3PS4 except the bulk modulus. Finally, the Debye temperature theta(D) and minimum thermal conductivity k(min) are 290.7 K (275.5 K) and 0.61 Wm(-1) K-1 (0.58 Wm(-1) K-1) for alpha-Na3PS4 (beta-Na3PS4). (C) 2019 The Electrochemical Society.