LAGP (Li1.5Al0.5Ge0.5P3O12) is a promising solid-state electrolyte (SSE) for all solid-state lithium-ion batteries (ASS-LIBs) with its favorable lithium ionic conductivity and good performance on inhibiting lithium dendrite. However, the ultrahigh interfacial resistance between lithium metal anode and LAGP SSEs greatly hinders its application. In this work, a thin film of metallic Bi was sputtered on LAGP to improve the chemical/physical properties of the Li/SSE interface. It is found that the Bi buffer not only inhibits the unfavorable reaction between LAGP SSEs and Li metal, but also improved their compatibility. As a result, the Li/LAGP interfacial resistance was effectively reduced from 2255.6 to 92.8 Ω cm2 at 30 °C. Furthermore, a good performance solid state full cell with a LiFePO4 cathode had been demonstrated. This work provides an effective avenue to address the interfacial challenges between Li metal and LAGP SSE.