A novel aqueous alkaline gel polymer electrolyte (GPE) was obtained by combining cotton with PVA, offering a wide operating electrochemical window (1.6 V) for aqueous supercapacitors (SCs). The effects achieved can be explained that the free water is limited inside GPE by strong hydrogen bonds, and hydrate cations and hydrate anions change into small free ions, so the obtained GPE appears improved electrochemical stability. The synthesized cotton/PVA-based membrane with weight ratio of 8:1(C/PCA-8-1) possesses high porosity (55%), liquid electrolyte uptake (771.43 wt%) and superior ionic conductivity (28 mS cm(-1)). The SC based on cotton and PVA with weight ratio of 8:5(C/PVA-8-5) soaking in KOH solution, owing to the best electrochemical performance, with the specific capacitance up to 160 F g(-1) at 0.5 A g(-1), and a higher specific energy of 11.8 Wh kg(-1). The flexible SCs based on cotton/PVA GPE can be bent to 180 degrees easily and still have good electrochemical performance. These results indicate that this kind of GPE can apply to wearable energy storage devices.