The NASICON-type ceramic Li1·5Al0.5Ge1.5(PO4)3 (LAGP) electrolyte has been proposed as the most competitive candidates of electrolyte materials toward solid-state Li metal batteries (LMBs) by reason of its high ionic conductivity, cyclic stability under extreme temperatures and wide voltage window. However, poor interface contact, high interfacial resistance and intractable mechanical properties greatly limit its practical applications. In this work, an inorganic-polymer “LAGP in PVDF” quasi-solid-state electrolyte (QSSE) is developed via solution casting method, in which pyr14TFSI ionic liquid (IL) and LiTFSI are combined as functional wetting interface. Benefiting from the coherent interaction of LAGP nanoparticles incorporated into the polymer matrix, and inherent protection of IL, the overall performance of the optimized QSSE include thermal stability, dense structure, flexibility and electrochemical properties. The XRD, SEM, XPS tests demonstrate that the IL using as a solid/electrolyte modified interlayer can enhance Li+ transport, interfacial infiltration and homogenize lithium deposition. The LiFePO4|PL-25LAGP|Li solid-state battery presents an excellent circulation performance under ambient temperature, which displayed an initial discharge specific capacity of 146.8 mAh g−1 at 0.5C and capacity retention of 96.25 % after 150 cycles. The flexibility PL-LAGP CSE shows superior safety and greater development potential for the “LAGP in PVDF” composite electrolyte in solid state LMBs.