Abstract: A cellulose-based all-solid-state polymer electrolyte separator, a preparation method thereof and an application thereof are provided. The cellulose separator is used as a skeleton, and solid-state polymer electrolyte is injected into pores of the separator using atomic layer deposition and dipping-coating processes. In addition, the polymer electrolyte remains in an amorphous structure at high temperatures by using an instantaneous quenching method, and ionic conductivity of the solid-state polymer electrolyte at room temperature is improved. After a surface of the solid-state polymer electrolyte separator is further coated with an alumina nanolayer, an electrochemical window width of the separator is significantly increased, and the solid-state polymer electrolyte separator is prevented from decomposing under a high voltage.