The invention provides a cellulose polymer electrolyte membrane, and a preparation method and application thereof. According to the invention, cellulose is used as a raw material, so the membrane has high porosity, electrolyte absorption performance and electrolyte retention performance due to reassembling of molecular structures of cellulose and a great amount of mesoporous structures among the molecular structures and is thus improved in ionic conductivity; and the membrane has good mechanical properties due to action of a great number of hydrogen bonds among the molecular chains of cellulose and formation of a three-dimensional homogeneous system. The cellulose polymer electrolyte membrane provided by the invention can be repeatedly folded, has good surface flexibility and transparency, abundant mesoporous structures and adjustable pore diameters; the pore diameters become larger and more uniform with prolongation of humidification time; the cellulose polymer electrolyte membrane porosity of 71.78%, ionic conductivity of 0.325 s/cm and good mechanical properties. As the cellulose polymer electrolyte membrane provided by the invention is applied to a flexible all-solid-state supercapacitor and a minisized supercapacitor, the membrane has good electrochemical performance and the prepared supercapacitors have scalability.