Room-temperature sodium‑sulfur (RT Na-S) battery is a promising candidate for large-scale energy storage applications due to its high theoretical specific energy, low cost, and environmental benefits. Here the effect of fluoroethylene carbonate (FEC) as an additive in 1.0M NaClO4-ethylene carbonate/propylene carbonate (EC/PC, V/V=1/1) electrolyte was verified in RT Na-S battery with a high-surface-area carbon/sulfur composite (YP50F/S) as the cathode. Using 1.0M NaClO4-EC/PC electrolyte containing 5wt% FEC, the YP50F/S electrode can deliver a reversible capacity of up to 1651mAhg−1 at 0.1C. When 5wt% FEC-added electrolyte is used, X-ray photoelectron spectroscopy (XPS) analysis of the electrode surface clearly indicates a more effective solid electrolyte interface (SEI), a more thorough transformation between S and Na2S, and a more obvious redox reaction between sulfur oxides during the first discharge-charge processes. We further confirm that 5wt% FEC can also be employed for another activated carbon material (XFP01), therefore, our work may provide a new insight for the development of RT Na-S battery.