<p>Solid-state sodium batteries offer new opportunities for emerging applications with sensitivity to safety and cost. However, the prevailing composite electrolyte structure, as a core component, is still poorly conductive to Na ions. Herein, a 3D architecture design of Na⁺ conductive Na₃Zr₂Si₂PO₁₂ framework is introduced to in situ compound with polymer electrolyte, subtly inducing an anion-enriched interface that acts as rapid ion immigration channel. Multiple continuous and fast Na⁺ transport pathways are built via the amorphization of polymer matrix, the consecutive skeleton, and the induced anion-adsorbed interface, resulting in a high ionic conductivity of 4.43 × 10⁻⁴ S·cm⁻¹. Notably, the design of 3D skeleton not only enables the content of inorganic part exceeds 60 wt% without any sign of agglomeration, but also endows the composite electrolyte reach a high transference number of 0.61 by immobilizing the anions. The assembled quasi-solid-state cells exhibit high practical safety and can stably work for over 1500 cycles with 83.1% capacity retention. This tactic affords new insights in designing Na⁺ conductive composite electrolytes suffering from slow ion immigration for quasi-solid-state sodium batteries.</p> Graphical abstract <p></p>