Medium-/high-entropy alloys (M/HEA) have attracted immense attention as a promising class of hydrogen-storage media thanks to their superior hydrogen-storage properties, i.e., high hydrogen to metal (H/M) ratio (e.g., up to 2.5) and excellent hydrogenation/dehydrogenation kinetics. However, the underlying microstructure evolution and corresponding hydrogen occupancy in the crystal structure remain not well understood during hydrogen-M/HEA interactions. In this study, in-situ high-energy X-ray diffraction was employed to capture the time-resolved microstructure evolution of a TiNbZr MEA during the hydrogen charging process at ambient pressure. The phases were identified and quantified using the Rietveld refinement method. The lattice parameters of individual phases were further analyzed to calculate the amount of stored hydrogen in the crystal lattice. In addition, electron backscatter diffraction and transmission electron microscopy techniques were used to characterize the lattice distortion of the MEA upon hydrogen charging. The hydrogen-MEA interaction and configuration were further discussed with the aid of the density functional theory. Such an in-depth understanding of hydrogen-metal configuration provides valuable insights into the hydrogenation process and new strategies to advance the design of hydrogen-storage metallic alloys.