The　construction　of　photocatalytic　systems　with　contact　interfaces　is　one　of　the　crucial　steps　toward　the　efficient　charge　separation　in　photocatalytic　reactions.　Here,　in-situ　growth　method　was　utilized　to　simultaneously　obtain　ultrathin　CuO　and　TiO2　nanosheets　with　contact　interfaces.　The　H2　yield　of　the　optimized　photocatalyst　is　∼　19.8　mmol/g,　∼　100　times　higher　than　that　of　TiO2.　In　contrast,　the　samples　prepared　by　physical　mixing　method　only　show　an　H2　yield　of　∼　3.2　mmol/g,　fully　demonstrating　the　highly　efficient　charge　separation　in　in-situ　prepared　samples.　In-situ　X-ray　photoelectron　spectroscopy　(XPS)　demonstrates　the　reversible　variation　of　metal　valence　states　and　their　band-edge　shift.　This　work　delivers　a　new　perspective　to　observe　the　real-time　behavior　of　metal　valances　in　photocatalysts　under　light　irradiation,　which　facilities　to　have　a　deep　understanding　of　photocatalytic　reactions.　©　2023　Elsevier　B.V.