Graphene-based　photodetector　with　ultra-high　responsivity　is　an　important　research　field　of　low　dimensional　optoelectronics　applications.　A　number　of　hybrid　graphene/quantum　dots　photodetectors　with　high　responsivity　have　been　developed.　In　this　paper,　the　in-situ　oxidation　of　the　copper　covered　by　monolayer　graphene　was　studied　under　the　oxygen-rich　condition.　It　is　found　that　the　oxidation　process　first　occurs　at　the　grain　boundary　of　graphene　and　the　oxide　is　Cu2O.　The　intensity　ratio　of　2D　band　and　G　band　of　graphene　is　similar　to　3,　and　the　defect　D　peak　is　absent,　which　indicates　that　the　quality　of　graphene　is　not　damaged　during　the　oxidation　process.　The　hybrid　transfer-free　graphene/Cu2O　photodetector　is　fabricated　by　in-situ　copper　oxidation.　Under　450　nm　laser　illumination,　the　responsivity　of　the　photodetector　is　3.8x10(6)　A/W　at　0.2　V.　The　gain　is　up　to　1.1x10(7),　which　is　due　to　the　modulation　of　Fermi　level　of　graphene　by　Cu2O　quantum　dots.　The　photodetector　exhibits　the　specific　detectivity　of　3.6x10(11)　Jones.　This　work　opens　a　feasible　pathway　to　develop　transfer-free　graphene/semiconductor　photodetector　with　high　responsivity.