The development of efficient electrocatalysts for saline water oxidation (SWO) is imperative for advancing seawater splitting technology to produce green hydrogen. In this work, we report a NiFeCo hydroxychloride pre-electrocatalyst with the merits of high surface area and anti-corrosion, which exhibited both active and stable SWO performance. The lattice Cl⁻ of NiFeCo hydroxychloride was leached during catalysis, leading to the 35.4% enlarged surface area of the catalysts, which showed a SWO overpotential of 369 mV at 100 mA·cm⁻², which is 105 and 154 mV lower than that of the NiFeCo layered double hydroxide and commercial RuO₂ catalysts, respectively. Moreover, in-situ Raman demonstrated the incorporation of electrolyte Cl⁻ to the lattice of the catalysts and the re-formation of Co–Cl bonds, which resulted in the enhanced anti-corrosion performance and high electrocatalytic stability for 100 h. These results provide a convincing demonstration of the reconstruction of ternary hydroxychloride pre-electrocatalysts for efficient seawater splitting hydrogen production.