A novel and green method to prepare porous membrane is reported by simply blending methylcellulose (MC) and lithium polymethacrylic acid (LiPMA) in water. Thanks to the coordination between oxygen atom in MC and Li+ in LiPMA and subsequent micro-phase separation between them, a porous membrane can be obtained after water evaporated. A series of membranes with different pore size and morphology are prepared by controlling the mass ratio of MC/LiPMA. All the membranes exhibit good thermal and electrochemical stability. With the increasing proportion of LiPMA, the obtained membrane has higher electrolyte uptake, resulting in higher ionic conductivity of corresponding gel polymer electrolyte (GPE). When the mass ratio is 5:20, the membrane has the highest the lithium ion transference (0.57), and the GPE reveals the higher ionic conductivity of 0.65 mS cm(-1) at room temperature. What's more, the aforementioned GPE exhibits excellent discharge capacity and good cycling performance. Without use of any organic solvents and tedious preparation process, this novel method is environmentally friendly and low-cost, and the obtained GPE exhibits excellent performance, which has a greatly commercial potential.