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Green hydrogen is a clean energy, and its application scenarios have become increasingly diverse with the development of hydrogen energy equipment. To ensure the safe use of hydrogen, it is essential to study the leakage and dispersion characteristics of hydrogen in different spaces. In this work, the experimental and numerical simulation studies on hydrogen leakage and dispersion were conducted in spaces with large aspect ratios. The research found that hydrogen leakage and dispersion can be divided into three typical stages: buoyancy-dominated stage, horizontal spreading stage, and vertical filling stage. The relationship between the concentration rise rate of hydrogen and the leakage rate and leakage direction in the third stage is established. As the leakage speed increases, the dispersion time of hydrogen decreases, leading to significant differences in concentration distribution. Changes in the leakage direction will influence the interaction between hydrogen and the walls, subsequently altering the dispersion behavior of hydrogen. Changes in leakage speed and direction do not affect the sequence of hydrogen dispersion to specific points in space. Based on the characteristics of hydrogen dispersion, a subjective-objective integrated hydrogen weighted concentration calculation method was proposed in this study. The hydrogen weighted concentration can be effectively characterized the leakage and dispersion characteristics of hydrogen. The value always approaches 50% of the average concentration, which can be used for determining the warning threshold or specifying emergency strategies. • The hydrogen dispersion process consists of three stages in large aspect ratio space. • The hydrogen dispersion sequence to a point unaffected by leakage rate and direction. • The hydrogen concentration rise rate model during linear rise is given. • A subjective-objective combined weighted concentration calculation method is given. [ABSTRACT FROM AUTHOR]