All-solid-state sodium-ion batteries are emerging as a highly promising substitute for lithium-ion batteries, primarily owing to their rich natural resources and superior safety performance. Solid electrolytes are integral components of all-solid-state batteries and have attracted much attention due to their remarkable safety and chemical stability. This study examines a novel solid electrolyte Na3(WSn)xSb1−2xS4 by modifying the W/Sn ratio and achieves a high ionic conductivity of 11.3 mS cm−2 at room temperature. Structural analysis demonstrates that the inclusion of tungsten facilitates the formation of cubic phase Na3SbS4 by more sodium vacancies. Furthermore, the co-dopant Sn ensures pure cubic conductors by removing impurities WS2 and increasing the element solubility. This efficiently enhances the movement of sodium ions and promotes ion transportation. The W/Sn-optimized Na3SbS4 (NBS) electrolyte also exhibited stable cycling for about 323 hours, which is about eight times longer than the Na3SbS4 base electrolyte. The efficient enhancement of the critical current density demonstrated the improvement of the structural stability at the interface where sodium dendrites formed easily. The formed Na–Sn alloy provides a protective barrier for the normal transport of ions. In addition, the small release of H2S also proves the stability of the electrolyte structure. These characteristics make it a highly promising electrolyte material for all-solid-state electrolytes.