The　structure　and　electronic　state　of　the　active　center　in　a　single-atom　catalyst　undergo　noticeable　changes　during　a　dynamic　catalytic　process.　The　metal　atom　active　center　is　not　well　demonstrated　in　a　dynamic　manner.　This　study　demonstrated　that　Li　metal　atoms,　serving　as　active　centers,　can　migrate　on　a　C3N4　monolayer　or　between　C3N4　monolayers　when　exposed　to　light　irradiation.　This　migration　alters　the　local　coordination　environment　of　Li　in　the　C3N4　nanosheets,　leading　to　a　significant　enhancement　in　photocatalytic　activity.　The　photocatalytic　H2O2　process　could　be　maintained　for　35　h　with　a　920　mmol/g　record-high　yield,　corresponding　to　a　0.4%　H2O2　concentration,　which　is　far　greater　than　the　value　(0.1%)　of　practical　application　for　wastewater　treatment.　Density　functional　theory　calculations　indicated　that　dynamic　Li-coordinated　structures　contributed　to　the　superhigh　photocatalytic　activity.