The　process　of　CO2　reduction　by　H2O　is　always　restricted　due　to　its　non-spontaneous　in　thermodynamic.　In　this　work,　a　photo-thermal　coupled　device　is　designed　to　obtain　a　high-achievement　CO2　methanation　by　H2O　over　carbon　dots　(CDs)　drafted　Cu/TiO2　(Cu/TiO2-C).　Dramatic　promotion　of　CH4　production　exhibits　under　UV　irradiation　at　a　higher　temperature　(＞　150　degrees　C),　but　a　poor　photo-promotion　at　room　temperature.　In-situ　diffuse　reflectance　infrared　Fourier　transform　spectroscopy　(DRIFTS)　and　isotopic-label　temperature　programmed　surface　reaction　(TPSR)　suggest　that　CO2　methanation　process　over　Cu/TiO2-C　can　be　regarded　as　two　main　spontaneous　process:　CO2　is　firstly　reduced　by　Cu(I)　(Cu2O)　to　CO　(CO2　+　Cu2O　-＞　CO　+　CuO),　then　CO　is　reduced　by　H2O　to　CH4　via　water-gas　shift　(WGS)　process.　Here,　CDs　not　only　act　as　electron　storage　to　keep　the　presence　of　Cu(I)　(from　Cu(II)　to　Cu(I)　not　to　Cu　(0))　at　a　high　temperature,　but　also　capture　the　photo-generated　holes　from　TiO2　induced　by　UV　light,　resulting　in　the　cycle　of　Cu(I)/Cu(II)　with　concomitant　of　electron　storage　and　release.　The　synergy　effect　of　UV　light　and　temperature　do　not　occur　on　the　Cu/TiO2　sample　without　CDs.　Here,　Cu　(II)　is　mainly　reduced　by　H-2　pretreatment　to　Cu　(0),　while　the　poor　cycle　of　Cu(I)/Cu(II)　was　exhibited　under　UV　irradiation.　This　study　shows　that　this　non-spontaneous　reaction　could　be　designed　as　two　ongoing　spontaneous　processes　by　adding　UV　light,　this　approach　may　apply　to　other　photo-thermal　reactions.