Magnesium/sulfur battery (Mg/S) has recently received wide attention due to its high theoretical energy density (3,260 Wh/L) and lowcost.To further improve its safety and flexibility,developing a polymer electrolyte that can be compatible with both electrophilic S endMg is critical.Here,we report a magnesium chloride-(fluorinated tetraethylene glycolic)borate (MgCl-FTGB) based non-nucleophilic,gel-type polymer electrolyte for Mg/S battery via a facile synthetic method through commercially available reagents.This electrolytecoupled with glass fiber allows reversible Mg deposition/dissolution (100％ coulombic efficiency) with low polarization (500 μA/cm2,300/300 mV),and shows a wide electrochemical window of 4.8 V (vs.Mg/Mg2+).Mg/S battery assembled with this electrolyte cancycle over 50 times with a high specific discharge capacity retention of over 1,100 mAh/g.