Using　environmental　scanning　transmission　electron　microscopy　and　a　global　optimization　algorithm,　we　unraveled　the　preoxidation　dispersion　and　direct　dispersion　mechanisms　in　Pd-CeO2(100)　systems,　mediated　by　the　behaviors　of　highly　dispersed　Pd　species.　At　lower　temperatures,　Pd　nanoparticles　first　undergo　oxidation,　followed　by　the　dispersion　of　PdO　nanoparticles.　In　contrast,　at　higher　temperatures,　Pd　nanoparticles　directly　convert　into　highly　distributed　cationic　Pd　species.　These　distinct　dispersion　mechanisms　are　driven　by　the　thermodynamic　and　kinetic　differences　of　environment-dependent　Pd1-2O　and　Pd1-4O　species,　providing　a　fundamental　basis　for　precisely　controlling　catalyst　dispersion　states.