Abstract: Direct seawater electrolysis is a strategic technology for realizing the large-scale green energy transition, but the long-term stability of the cathode under authentic marine working conditions remains a core bottleneck restricting its industrialization. Currently, this technology faces two major challenges: inorganic salt scaling and structural instability induced by start-stop fluctuations. Addressing these bottlenecks, this review systematically summarizes multiscale stability-enhancement strategies for catalytic systems. Regarding anti-scaling, it outlines synergistic defense mechanisms including morphological self-cleaning, dynamic microenvironment regulation, interfacial ion barriers, and macroscopic reactor system engineering. In terms of anti-fluctuation deactivation, it analyzes structural stabilization strategies to mitigate reverse current shocks, such as in-situ dynamic passivation, microenvironmental electrostatic shielding, heterogeneous anchoring, and spatial confinement. Comparative analysis reveals that local mass transfer polarization at high current densities and the whole-cell short-circuit galvanic effect under extreme variable-load conditions are common technical bottlenecks. The effectiveness of anti-scaling and anti-fluctuation strategies highly depends on the operating current range and the hydrodynamic characteristics of the electrolyte flow field. Future breakthroughs rely on cross-scale synergistic designs integrating microscopic active site protection with macroscopic reactor flow field management. Finally, engineering design criteria for durable cathodes are extracted, and the prospects of multi-element co-extraction of inorganic substances and data-driven discovery are discussed, aiming to provide an academic reference for large-scale and sustainable hydrogen production from seawater.