Step heating experiments on ultra-high pressure (UHP) rocks from the Dabie Mountain shows a majority of CO2 in fluid inclusion (excluding H2O) ; CO is also a significant component, with a small content of N2 and CH4 Carbon isotopic composition of CO2 in fluid of metamorphic climax stage ( - 25‰- - 30‰) is different from that of mantle carbon, indicating that UHP rocks did not experience obvious transformation by mantle fluids despite their subduction depth. CO2 was derived from carbon matter in the protoliths of UHP rocks in a relatively confined system, showing that the UHP rocks subsided quickly and uplifted quickly from the mantle. Step heating experiments on ultra-high pressure (UHP) rocks from the Dabie Mountain shows a majority of CO2 in fluid inclusion (excluding H2O); CO is also a significant component, with a small content of N2 and CH4 Carbon isotopic composition of CO2 in fluid of metamorphic climax stage (- 25 ‰ - - 30 ‰) is different from that of mantle carbon, indicating that UHP rocks did not experience obvious transformation by mantle fluids despite their subduction depth. CO2 was derived from carbon matter in the protoliths of UHP rocks in a relatively confined system, showing that the UHP rocks subsided quickly and uplifted quickly from the mantle.