Silk/polyethylene oxide composite solid polymer electrolyte was prepared by casting polyethylene oxide (PEO) and lithium salt solution on silk and drying it into a film with natural silk as the skeleton supporting material. The structure and properties of the solid polymer electrolyte were characterized by FT-IR, tensile tester, synchronous thermal analyzer, electrochemical window test, conductivity test, etc. The battery was assembled with lithium iron phosphate as the positive electrode and lithium metal as the negative electrode to test the charging and discharging performance. The results show that the composite solid polymer has better mechanical strength (up to 10 MPa) and an excellent electrochemical window (up to 4.6 V) compared with the conventional PEO solid polymer electrolyte. The specific capacity of all-solid-state lithium batteries assembled with the electrolyte reaches 113 mAh/g at 60℃and 1C current density, and the capacity retention rate reaches 97% after 100 cycles, showing excellent cycle stability.