The quasi-solid electrolyte membranes (QSEs) are obtained by solidifying the precursor of unsaturated polyester and liquid electrolyte in a glass fiber. By modifying the ratio of tetraethylene glycol dimethyl ether, QSE with balanced ionic conductivity, flexibility, and electrochemical stability window is acquired, which is helpful for inhibiting the decomposition of electrolyte on the cathode surface. The QSE is beneficial to the interfacial reaction of Li + , electrons, and O 2 in the quasi-solid lithium-oxygen battery (LOB), can reduce the crossover of oxygen to the anode, and extend the cycle life of LOBs to 317 cycles. Benefitting from the application of QSE, a more stable solid electrolyte interface layer can be constructed on the anode side, which can homogenize Li + flux and facilitate uniform Li deposition. Lithium-oxygen pouch cell with in situ formed QSE 2 works well when the cell is folded or a corner is cut off. Our results indicate that the QSE plays important roles in both the cathode and Li metal anode, which can be further improved with the in situ forming strategy.