Lithium-sulfur (Li-S) battery is one of the promising high-energy battery systems for future use. However, the shuttle effect due to the dissolved lithium polysulfides in ether electrolyte hampers its practical application. Applying electrolyte additives in Li-S battery has been widely acknowledged as an effective way to reduce the shuttle effect and improve cycling efficiency. In this work, benzoselenol (PhSeH) is used as an organic electrolyte additive in Li-S battery. It reacts with elemental sulfur to form phenyl selenosulfide, altering the redox pathway of the cathode with the regeneration of S8 at the end of charge and enabling new redox reactions with high reversibility. The Li-S coin cell with an optimized amount of PhSeH in the electrolyte delivers a high discharge capacity of 1,436 mAh·g−1 and a capacity retention of 92.86% in 200 cycles, and exhibits lower discharge overpotential in comparison to the cell with blank electrolyte. The Li-S pouch cell with a low electrolyte/sulfur (E/S) ratio of 4.0 μL·mg−1 shows a discharge capacity of 1,398 mAh and excellent capacity retention for 20 cycles.