Facing global energy and environmental challenges, hydrogen is seen as a crucial clean energy carrier. Conventional water electrolysis is hindered by the sluggish kinetics of the anodic oxygen evolution reaction (OER). Replacing OER with the hydrazine oxidation reaction (HzOR) offers a much lower theoretical potential (−0.33 V vs. reversible hydrogen electrode (RHE)), faster kinetics, and the production of only N₂, eliminating explosion risks from H₂/O₂ mixtures. Achieving high-performance hydrazine-assisted water splitting requires advanced electrocatalysts that efficiently drive both the hydrogen evolution reaction (HER) at the cathode and HzOR at the anode. Interface engineering, constructing and modulating the interfaces between different material components, has emerged as a powerful strategy to optimize catalyst properties. By precisely designing interfaces, researchers can synergistically tune electronic structures, expose more active sites, facilitate charge transfer, and enhance stability. The review first outlines the fundamental mechanisms of HER and HzOR, introducing key descriptors like hydrogen adsorption free energy (ΔG_*H). It then discusses advanced characterization techniques essential for probing interfacial structures and in situ/operando methods. The core of the article focuses on major interfacial engineering strategies, which includes vacancy defects, doping, heterostructures, and strain engineering. Each strategy is illustrated with recent exemplary catalysts, demonstrating how interface design leads to superior HER/HzOR bifunctional activity, high current density at low cell voltages, and remarkable long-term durability. The review concludes by highlighting the progress made and future challenges in developing practical, high-performance catalysts for this energy-saving hydrogen production technology.