The implementation of succinonitrile (SN)-based polymeric deep eutectic electrolytes (SN-PDEEs) in sodium metal batteries remains challenging due to the high reactivity of sodium metal, which leads to severe interfacial instability between the electrolyte and anode. Herein, we develop a novel PDEE system by synergistically integrating polyethylene glycol diacrylate (PEGDA) with fluoroethylene carbonate (FEC) to achieve substantially improved interfacial compatibility. The cross-linked PEGDA network physically confines SN molecules, while FEC preferentially decomposes to construct a robust, fluorine-rich solid electrolyte interphase (SEI), as unambiguously evidenced by XPS depth profiling which shows intense NaF signals and FEC-derived -CHF-OCO₂- species while suppressing SN reduction. The optimized PDEE exhibits a commendable ionic conductivity of 0.76 mS cm⁻¹ and a high sodium ion transference number of 0.72. The P-5%F-PDEE endows the symmetric Na/Na cell with a small polarized potential and outstanding long-term cycling performance over 800 hours at 25 °C. When assembled in an Na₃V₂(PO₄)₃ (NVP)||Na cell, it maintains 92% capacity retention after 500 cycles at 0.5 C. Moreover, in an Na₃V₂(PO₄)₂F₃ (NVPF)||Na configuration cycled at 0.2 C with a high cut-off voltage of 4.2 V, possessing 89.4% capacity retention after 100 cycles. This work provides an effective synergistic strategy approach to improve the interfacial stability of PDEEs for dendrite free sodium metal batteries.