The present disclosure provides an electrolyte liquid of a lithium sulfur battery comprising a carbonate ester organic solvent, a lithium salt, and a flame-retardant cosolvent, the flame-retardant cosolvent being a phosphazene compound, wherein a mass percentage of the flame-retardant cosolvent is 20% to 50%, a concentration of the lithium salt is 0.8 mol/L to 1.2 mol/L. The present disclosure also provides a lithium sulfur battery and a method for preparing the electrolyte liquid.