<p>Aqueous zinc-ion batteries are promising candidates for large-scale energy storage, yet their development is severely hindered by the interfacial instability of zinc anodes. Distinct from strategies employing pre-formed polymers, this work proposes an innovative monomer-induced in situ interface engineering strategy. By leveraging the preferential adsorption of acrylamide monomers on the Zn surface, a locally high-concentration region is created, which subsequently enables the in situ construction of a stable hydrated network interphase (HNI) triggered synergistically by Zn²⁺ and SO₄²⁻ during electrochemical cycling. The HNI precisely regulates Zn deposition via a triple synergistic mechanism: Lewis acid–base coordination (C = O···Zn²⁺) provides fixed nucleation sites; dynamically anchored SO₄²⁻ within the interphase forms negatively charged microregions that homogenize Zn²⁺ flux via Coulombic repulsion; and a dense hydrogen-bonding network effectively confines free water and suppresses side reactions. Benefiting from this multifunctional interphase, the Zn//Zn symmetric cell achieves an ultra-long cycling life of 8650 h (over 360&#xa0;days) at 1&#xa0;mA&#xa0;cm⁻² with excellent reproducibility, the Zn//Ti cell delivers a high average Coulombic efficiency of 99.71% at 5&#xa0;mA&#xa0;cm⁻². The Zn//I₂ full cell retains 89.15% of its capacity after 12,000 cycles. This work provides a novel paradigm for interfacial construction toward high-performance zinc metal anodes.</p><p></p>