Developing efficient and durable electrocatalyst for seawater splitting is crucial in hydrogen production. Herein, a multi‐scale design strategy was employed to fabricate ruthenium clusters modification carbon layer‐encapsulated nickel‐cobalt‐phosphorus (Ru/C/NiCoP) nanoneedles electrocatalyst supported on nickel foam (NF). We demonstrated that Ru/C/NiCoP/NF exhibited exceptional oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) performances, with low overpotential, Tafel slope and superior stability. Furthermore, the electrocatalytic mechanism of Ru/C/NiCoP was elucidated through the combination of ex‐situ and in‐situ characterizations, along with comprehensive electrochemical tests. Strikingly, Ru clusters and the NiCoP with carbon layer engendered robust electronic interaction reaction, accelerated the charge transfer rate, provided more active sites, and enhanced intrinsic catalytic activity, thus substantially promoting the OER kinetics and HER reaction steps as well as stability. In addition, the two‐electrode system constructed with Ru/C/NiCoP/NF achieved current density of 10 mA cm−2 in both pure water and seawater at ultra‐low potential of 1.46/1.47 V, with Faraday efficiency close to 100 %. Even at higher current density of 100 mA cm−2, the required driving voltage remained low at 1.75/1.77 V, maintaining stable operation for 150 h, outperforming most reported non‐noble catalysts. This innovative strategy provides facile and versatile approach for developing advanced electrocatalysts in seawater electrolysis application.