Abstract: Yttrium, as an important member of rare earth metals, its hydride, hydrogenated yttrium (YH_x), due to its excellent high-temperature thermal stability, high hydrogen density, and small neutron absorption cross-section, has become an ideal candidate material for slow neutron moderators suitable for high-temperature, miniaturization, and lightweight new nuclear reactors. However, there is a gap in the hydrogen absorption kinetics data of yttrium in the 700-900 ℃ high-temperature range in existing research, and the correlation mechanism between the microstructure and hydrogen absorption rate has not been clarified. This paper takes pure metallic yttrium as the research object and conducts high-temperature hydrogen absorption kinetics experiments using the constant volume and pressure method. Data analysis was carried out using the first-order reaction model and Arrhenius equation, and the kinetic laws of hydrogen absorption reactions at high-temperatures were explored through the combination of metallographic characterization analysis systems. The main conclusions are as follows. Firstly, the hydrogen absorption reaction fraction (F) shows a rapid increase-slow stabilization parabolic characteristic over time in the initial stage, hydrogen atoms are rapidly adsorbed and react with the yttrium matrix, and F increases rapidly. In the later stage, due to the formation of the hydrogen compound layer and the increase in the resistance of hydrogen atom diffusion, the growth rate of F gradually slows down until equilibrium is reached. The temperature has a particularly significant effect on shortening the equilibrium time: pure yttrium (H/Y=0) has an equilibrium time of approximately 200 s at 700 ℃, 60 s at 800 ℃, and only 10 s at 900 ℃ for instant equilibrium; even for H/Y=1.3 with a higher hydrogenation degree, the equilibrium time at 900 ℃ is shortened from 1 700 s at 700 ℃ to 300 s, which is highly compatible with the core requirement of the nuclear reactor hydrogen purification system for rapid capture of hydrogen species. Secondly, the hydrogen absorption reaction of metal yttrium and its hydride more conforms to the first-order reaction kinetics model, and the fitting correlation coefficient R² is generally ≥0.98. At the same temperature, the reaction rate constant (k) decreases significantly with the increase in the H/Y ratio; While increasing the temperature can significantly increase the k, at 900 ℃, indicating that high-temperature can effectively break through the diffusion barrier of hydrogen atoms in the yttrium matrix. Thirdly, based on the Arrhenius equation, the activation energy of the hydrogen absorption reaction of metal yttrium in the 700-900 ℃ range is 138.008 kJ/mol. Fourthly, the hydrogen absorption phase transition follows the process of α-Y→α-Y+δ-YH_x→δ-YH_x, with the grain boundaries being the preferred nucleation sites of the δ-YH_x phase. This study fills the gap in high-temperature hydrogen absorption kinetics data, clarifies the rate control mechanism, and provides key data support for the application of yttrium-based materials in high-temperature hydrogen storage systems and nuclear reactors.