Abstract: The thermodynamic and kinetic properties of body-centered-cubic (BCC) hydrogen storage alloys highly depend on their chemical compositions, making high-entropy alloying a promising strategy for performance optimization. However, clarifying how multi-principal element compositions regulate multiscale structures and thereby influence their hydrogen storage performance, limiting the rational design of high-performance BCC high-entropy alloys (HEAs), remains a challenge. This review provides a comprehensive overview of the recent advances in BCC HEAs for hydrogen storage, with emphasis on the multiscale regulation of their thermodynamics and kinetics. Empirical descriptor-guided composition screening, thermodynamic modeling based on the CALculation of PHAse Diagrams, and data-driven and machine learning-assisted approaches are discussed. In addition, the roles of melting-based processing, mechanical alloying, and emerging fabrication strategies in controlling the chemical homogeneity, defect structures, and microstructural stability of materials are examined. The hydrogen storage performance is analyzed in terms of activation behavior, thermodynamics, kinetics, and cyclic stability, with a focus on the underlying governing factors and mechanistic origins. Finally, prospective challenges and research directions are outlined to guide the design and processing of BCC HEAs.