Hydrogen is a critical renewable energy source in the energy transition. However, water electrolysis, which is the primary technique for achieving large-scale and low-carbon hydrogen production, still suffers from high production costs and energy consumption. The key is to develop highly efficient electrochemical water splitting catalysts. In recent years, the preparation of electrocatalysts via plasma treatment has gained recognition for its rapid, eco-friendly, and controllable properties, especially in the optimization of nano-microstructure. This review comprehensively summarized the impact of plasma treatment on the nano-microstructure of water electrolysis catalysts, encompassing dispersion enhancement, morphology modulation, surface functionalization, defect construction, and element doping. These impacts on the nano-microstructure increase the surface area, modify the pore structure, introduce active sites, and regulate the electronic environment, thereby promoting the water splitting performance of electrocatalysts. Finally, the remaining challenges and potential opportunities are discussed for the future development of plasma treatment. This review would be a valuable reference for plasma-assisted electrocatalyst synthesis and mechanism understanding in plasma impact on nano-microstructure.