Compared to Li-ion batteries, Na-ion batteries hold significant advantages and market value for achieving low-cost and large-scale energy storage, thanks to the utilization of cheap and abundant Na resources. However, the use of highly flammable liquid electrolytes with leaky risk raises safety concerns for conventional Na-ion batteries under abuse conditions such as mechanical damage, short-circuiting, and thermal runaway. Limited electrochemical stability of liquid electrolytes also hinders further enhancement of the performance of Na-ion batteries for practical use. This study reports a facile way for the preparation of high-performance gel polymer electrolyte (GPE) by thermal-driven radical in-situ polymerization of dipentaerythritol penta-/hexa-acrylat (DPEPA). This GPE exhibits an ionic conductivity of 1.97 mS·cm^-1, a Na⁺ transference number of 0.66, and a broad electrochemical stability window. The DPEPA displays a lower lowest unoccupied molecular orbit (LUMO) energy level than that of ethylene carbonate (EC) and diethyl carbonate (DEC) solvents, allowing for its preferential decomposition alongside NaPF₆ on the anode surface. This leads to a stable organic-inorganic composite film of solid-state electrolyte interphase, inhibiting the decomposition of electrolyte solvents on the anode surface. The quasi-solid-state Na-ion battery employing Na(Ni _1/3Fe_1/3Mn _1/3)O₂ (NFM) cathode and hard carbon (HC) anode in this GPE exhibits a high capacity retention rate of 92% after 300 stable cycles at a current density of 120 mA·g^-1, while achieving the specific capacities of 99-120 mAh·g^-1 within a wide temperature range of 20-80 ℃. In-situ X-ray diffractometer analysis reveals the highly reversible structural evolution of the NFM cathode during Na storage and the “adsorption-pore-filling” mechanism of Na⁺ storage in the HC anode. All data in this research demonstrates that introducing polymers with low LUMO energy levels proves an effective approach to enhance the electrochemical stability of solid-state Na-ion batteries while improving cell safety.