Developing cost-effective and high-performance bifunctional electrocatalysts is crucial for addressing the kinetic limitations of water electrolysis. Here, we successfully fabricate strained phosphorus-doped nickel-iron oxide on iron foam (P-NiFe₂O₄/IF) via simple corrosion-annealing coupling strategy. In situ Raman and electrochemical analyses reveal that the tensile lattice strain induced by P doping reorganizes the interfacial hydrogen-bond network and enhances its connectivity, accelerating proton transfer and deprotonation processes. Combined with theoretical calculations, it is confirmed that strain regulation effectively modulates the adsorption of *OH/*H, avoiding the *OH poisoning and poor deprotonation. In addition, the strain effect promotes surface reconstruction to generate active phases. Benefiting from the above advantages, P-NiFe₂O₄/IF exhibits excellent bifunctional electrocatalytic activity. A two-electrode electrolyzer constructed with P-NiFe₂O₄/IF requires only 1.45 V to reach 10 mA·cm^–2 and maintains outstanding operational durability even under high current conditions. This research sheds light on fabricating efficient and robust bifunctional electrocatalysts for water-splitting by regulating interfacial water and intermediate adsorption via strain engineering.