A comprehensive research coupling experiment and computation has been performed to understand the phase transition of Na3SbS4 and to synthesize cubic Na3SbS4 (c-Na3SbS4), a high temperature phase of Na3SbS4 that is difficult to be preserved when cooled down to ambient temperature. The formation of c-Na3SbS4 is verified by Rietveld refinement, nuclear magnetic resonance spectroscopy as well as electrochemical impedance spectroscopy. Unlike tetragonal Na3SbS4 (t-Na3SbS4) appearing phase transition at high temperature, c-Na3SbS4 is stable not just at room temperature but also sustaining thermal cycling up to at least 200 °C. Both experiment and theoretical calculation reveal that the ionic conductivity of c-Na3SbS4 is higher than that of t-Na3SbS4, though the values are in the same order of magnitude. Both structures allow fast ion transport. All-solid-state cells with c-Na3SbS4 solid electrolyte demonstrate superior Coulombic efficiency, high specific capacity, and relatively good cycling stability. Na3SbS4 solid electrolyte is promising for all-solid-state sodium-ion batteries.