AbstractAqueous zinc‐based energy storage systems (Zn‐ESSs) with intrinsic safety and good electrochemical performance are promising power suppliers for flexible electronics, whereas unstable zinc anodes especially in flexible Zn‐ESSs pose a challenge. Herein, a self‐assembled robust interfacial layer to achieve stable zinc anodes in non‐flexible and flexible Zn‐ESSs is reported. Specifically, zinc anodes and their slowly‐released Zn2+ simultaneously interact with tannic acid molecules in ethanol–water solutions, triggering the self‐assembly of a tannic acid/Zn2+ complex interfacial layer (CIL) that firmly anchors on the zinc anodes. The CIL containing abundant carboxyl and phenolic hydroxyl functional groups provides rich zincophilic sites to homogenize Zn2+ flux and accelerate Zn2+ desolvation‐deposition, and traps H+/H2O species to prevent them from corroding zinc anodes, thereby stabilizing the zinc deposition interface. Consequently, the CIL@Zn anodes present superior stability with an operation lifetime exceeding 700 h even at 5 mA cm−2 (28 times longer than that of bare zinc anodes) and ultrahigh cumulative plated capacity of ≈1.8 Ah cm−2. The firm anchoring of the CIL enables the CIL@Zn anodes to endure diverse deformations, thus realizing highly flexible CIL@Zn anode‐based Zn‐ESSs. This work provides thinking in designing stable and flexible zinc anodes, promoting the development of flexible zinc‐based energy storage.