Polymeric　carbon　nitride　(C3N4)　is　a　very　attractive　candidate　to　produce　photocatalytic　hydrogen　peroxide　(H2O2)　due　to　its　low-cost,　metal-free　characteristics.　However,　the　low　efficiency　would　limit　its　development　to　higher　yields　because　of　insufficient　light　absorption　and　electron-hole　separation.　Here,　we　developed　a　simple　method　to　anchor　CN　quantum　dots　(QDs)　onto　g-C3N4　nanosheets　to　form　a　homojunction　structure　(HJ-C3N4),　which　could　improve　photocatalytic　performance　largely　without　introducing　metal　elements.　Its　superior　efficiency　is　a　result　of　the　band　alignment　by　the　homojunction　structure　providing　excellent　electron-hole　separation　and　QDs　providing　suppressed　recombination.　Simultaneously,　the　light　responsiveness　of　QDs　endows　a　wide　spectrum-responsive　adsorption　and　enhances　the　adsorption　intensity.　The　H2O2　yield　of　the　HJ-C3N4　reached　115　mu　mol　L-1　h(-1)　in　pure　water　by　visible　light,　which　has　an　8.6x　higher　production　than　g-C3N4　nanosheets.　The　material　design　of　0D/2D　homojunction　could　be　extended　to　other　materials　with　specific　band　alignment.