A　typical　photocatalytic　H2O2　production　reaction　primarily　comprises　three　processes:　photoabsorption,　electron-hole　separation　and　transfer,　and　surface　oxygen　reduction　reaction.　Previous　researches　have　focused　on　revealing　the　origin　of　the　facet　effect　in　photocatalysis.　However,　a　comprehensive　under-standing　of　the　structure-activity　relationship　for　facet　effect　at　atomic　scale　remains　limited.　Herein,　we　provide　fundamental　insights　into　photocatalytic　H2O2　production　performance　of　three　types　of　TiO2　with　predominantly　exposed　(101),　(100),　or　(001)　facets.　The　TiO2　nanosheets　with　exposed　(001)　facet　exhibit　the　highest　H2O2　yield　rate　of　649.2　mmol　g-1　h-1,　which　is　29.2　and　5.2　times　higher　than　those　of　TiO2　with　(101)　facet　and　(100)　facet,　respectively.　Band　alignment,　charge　carrier　behavior,　and　surface　reaction　are　studied　systematically　and　correlated　with　unique　surface　atom　arrangement.　Even　with　narrowed　light-response　range,　short　charge　carrier　lifetime,　inferior　charge　separation,　and　inconspicuous　specific　surface　area,　the　(001)　facet　exposed　TiO2　still　performs　best.　The　experimental　results　and　density　functional　theory　(DFT)　calculations　reveal　that　the　under-coordinated　Ti　atoms　on　(001)　surface　serve　as　active　sites　and　have　strong　interaction　with　oxygen　molecule,　while　the　Ti　atoms　on　(101)　and　(100)　surface　can　hardly　adsorb　and　activate　oxygen　molecule.　Hence,　we　suggest　that　the　significantly　lowered　barrier　for　oxygen　molecule　adsorption　and　activation　results　from　intrinsic　surface　sites　rather　than　band-alignment,　and　the　charge　carrier　behavior　plays　the　principal　role　in　this　case.　This　work　may　provide　semiquantitative　insights　into　the　origin　of　facet　effect　in　photocatalysis.　(c)　2023　Elsevier　Ltd.　All　rights　reserved.