This research investigates active-site uniformity in single-atom catalysts (SACs) and its impact on catalytic performance. Active-site uniformity varies depending on synthetic methods, reaction conditions, and raw material compositions. These structural variations alter the coordination environment and electronic configuration of SACs, modulating adsorption behaviour and overall catalytic reactivity. X-ray absorption spectroscopy (XAS) is a key technique for characterising active sites via EXAFS and XANES spectra. In EXAFS mode, X-rays excite core electrons from a target atom, which are then scattered by neighbouring atoms; fitting these experimental data to theoretical models reveals interatomic distances. Meanwhile, XANES can be utilised to analyse oxidation states and electronic structures.