Solid-state lithium-ion batteries (LIBs) show significantly improved safety since they avoid the use of flammable liquid organic electrolytes in traditional LIBs. However, one of the most challenge issues for all solid state LIBs is the effective solid-solid interfacial contact and stability with repeated charges/discharges at electrode/separator interfaces. Ceramic separators are mechanically brittle and hard to process. The volume change of electrode materials during charges/discharges causes serious crack at electrode/separator interfaces. In comparison, polymer electrolyte membranes are flexible and easy to process, and are more feasible to solve the interfacial problem. In this work, a double-layered solid polymer separator is prepared to improve the stability of Li metal/solid separator interface. In the separator, one layer contacted with cathode is poly(vinylidene fluoride) (PVDF)/ Li_6.75La₃Zr_1.75Ta_0.25O₁₂ (LLZTO)/LiTFSI, which exhibits a room-temperature Li⁺ conductivity of 5 × 10⁻⁴ S cm⁻¹. The other layer close to Li metal is much thinner as compared with the first layer, which contains PVDF/LLZO/LiTFSI/graphene. Our results show that adding graphene into the separator can suppress Li dendrite and improve coulombic efficiency. Conductive graphene sheets in the separator not just stop mechanically the Li dendrite growth, but also allow the dendrite Li charge/discharge and avoid the presence of dead Li. By optimize the separator composition and parameters, the performance of Li metal based cells are improved significantly due to the improve electrode/separator interfacial stability.