The　stability　of　the　catalyst　has　always　received　considerable　attention　in　materials　science　and　catalysis.　Single　atom　site　catalysts　(SACs)　with　high　surface　energy　and　low　coordination　number　are　generally　believed　not　as　stable　as　nanocatalysts.　Herein,　we　discovered　that　nanocrystals,　such　as　nanowires　(NWs),　which　are　unstable　at　high　temperature,　can　be　directly　converted　into　SACs　without　undergoing　particles　aggregation　and　growth.　Insitu　environmental　transmission　electron　microscopy,　X-ray　absorption　spectroscopy,　and　density　functional　calculation　studies　demonstrated　that　the　high　temperature　overcomes　the　energy　barrier　of　metal　atomization　while　N-doped　carbon　materials　regulate　the　atomic　adsorption　energy,　both　of　which　jointly　cause　the　transformation　of　NWs　into　SACs.　Notably,　the　obtained　SACs　exhibited　excellent　catalytic　performance　for　the　hydrogenation　of　nitroarenes　to　the　corresponding　amines　due　to　the　considerable　decrease　in　energy　barriers　of　the　rate-determining　step.