One-pot　synthesis　of　urea　[(NH2)2CO]　from　easily　available　small　molecules,　that　is,　N2,　CO2,　and　H2O,　is　an　extremely　attractive　but　very　challenging　reaction.　2D-CdS@3D-BiOBr　composites　with　S-scheme　heterojunctions　are　constructed　via　a　facile　hydrothermal　technique　followed　by　a　self-assembly　method　and　shown　to　be　an　excellent　photocatalyst　enabling　the　reduction　of　N2　and　CO2　with　H2O　to　(NH2)2CO　under　visible　light.　The　optimal　40%2D-CdS@3D-BiOBr　sample　shows　up　to　15　μmol·g-1·h-1　total　yield　of　NH3　and　(NH2)2CO,　of　which　(NH2)2CO　accounts　for　54%.　The　apparent　quantum　efficiency　(AQE)　is　3.93%　for　urea　production.　On　the　photocatalyst,　urea　is　speculated　to　form　by　two　possible　chemical　routes.　One　is　direct　photocatalytic　synthesis.　Both　N2　and　CO2　molecules　are　activated　by　the　Cd2+　ion　of　2D-CdS　and　the　oxygen　defect　of　3D-BiOBr　at　the　edges　of　the　heterojunction　interface　of　2D-CdS/3D-BiOBr,　respectively.　*HNCONH*　is　the　key　intermediate　of　the　formation　of　(NH2)2CO　molecules.　The　other　is　indirect　synthesis　by　photocatalysis　and　then　thermocatalysis.　N2　is　reduced　into　NH3　and　CO2　is　reduced　into　CO　on　2D-CdS　by　the　photogenerated　electrons　and　protons,　and　then　the　formed　NH3　reacts　with　the　reactant　CO2　or　the　product　CO　to　form　(NH2)2CO　by　thermocatalysis　on　2D-CdS.　The　former　is　dominant　for　urea　synthesis.　The　work　confirms　that　urea　could　be　synthesized　photocatalytically　from　cheap　N2,　CO2,　and　H2O　under　visible　light.　A　composite　heterojunction　semiconductor　could　be　a　prospective　photocatalyst　appropriate　for　the　complex　reaction.　©　2023　American　Chemical　Society.