Rechargeable room-temperature (RT) sodium–sulfur (Na–S) batteries hold great potential for large-scale energy storage owing to their high energy density and low cost. However, their practical application is hindered by challenges such as polysulfide shuttling and Na dendrite formation. In this study, a dual salt-based quasi-solid polymer electrolyte (DS–QSPE) was developed via in situ polymerization, achieving high ionic conductivity (4.8 × 10⁻⁴ S·cm⁻¹ at 25 °C), a high sodium-ion transference number (0.73), and effective polysulfide confinement. Theoretical calculations and experimental results indicate that the enhanced Na-ion transport is attributed to the strengthened coordination of anions with the polydioxolane chain and the increased dissociation of sodium salts. Importantly, the DS–QSPE forms an interconnected network structure in the sulfurized polyacrylonitrile (SPAN) cathode. This provides abundant and seamless electrochemical reaction interfaces that facilitate efficient and uniform ion transport pathways. As a result, the Na||SPAN battery with DS–QSPE delivers a high capacity of approximately 327.4 mAh·g⁻¹ (based on the mass of SPAN) after 200 cycles at 0.2 A·g⁻¹, retaining 81.4% of its initial capacity. This performance considerably surpasses that of batteries using liquid electrolytes. This study offers a straightforward approach to addressing the interfacial challenges in solid-state Na–S batteries.