The origins of activity hysteresis during heating and cooling stages in CO oxidation are still heavily debated. Pt-CeO₂ and Pt-Al₂O₃ were observed to display completely different hysteresis phenomena. Pt-Al₂O₃ exhibited normal behavior, while Pt-CeO₂ showed inverse hysteresis. The affecting issues of initial Pt nanoparticle size, mass and heat transfer limitations, and local overheating were all excluded for both catalysts. By using operando and in situ characterization technologies, kinetic analyses, density functional theory (DFT) calculations, as well as ab initio molecular dynamics (AIMD) simulations, the nature of thermal hysteresis was revealed. The different interactions between the metal and supports induced different dynamic oxidation behaviors and morphology evolutions of Pt during the heating and cooling reactions, which are the root causes. Pt in Pt-CeO₂ suffered irreversible oxidation mainly driven by reverse oxygen spillover and formed Pt_xO_y ensemble which displays poorer activity. In contrast, Pt in Pt-Al₂O₃ underwent structural collapse and dispersion on Al₂O₃ surface at high temperature, and oxygen spillover to support preserved the initial chemical state of Pt.