Polymer–ceramic composite electrolytes hold great promise for high-performance, flexible all-solid-state lithium (Li) metal batteries. However, limited ionic conductivity and high interfacial impedance remain major obstacles to their commercial deployment. Herein, a dual-composite solid electrolyte was fabricated using a simple and innovative 3D printing approach, incorporating a polyvinylidene fluoride (PVDF)–Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) structural layer and a polyethylene oxide (PEO)–LLZTO interfacial modification layer. In this design, the PVDF matrix serves as a robust structural framework, while the LLZTO filler synergistically enhances ionic conductivity by promoting Li-salt dissociation and suppresses dendrite formation through improved mechanical strength, particularly at the Li-metal interface. The dense PEO–LLZTO layer on the opposing side ensures intimate contact with the cathode, minimizes interfacial side reactions, and optimizes interfacial electrochemical properties, thereby enabling stable and high-performance all-solid-state Li batteries. At 25°C, the dual-composite solid electrolyte exhibits a high ionic conductivity of 4.87 × 10⁻⁴ S·cm⁻¹ and a wide electrochemical stability window of 5.01 V. Leveraging this advanced electrolyte, Li||Li symmetric cells demonstrate stable Li plating and stripping for over 1200 h at 0.1 mA·cm⁻² without dendrite formation or short-circuiting. Correspondingly, LiFePO₄/Li full cells deliver excellent electrochemical performance, maintaining 98.2% capacity retention after 200 cycles. These results highlight that employing a dual-composite solid electrolyte is an effective strategy for mitigating interfacial challenges, thereby enabling the development of high-performance solid-state Li-metal batteries.