Abstract: The carbonaceous substance physically accreted with pyrite improves the floatability of coal-pyrite. In order to reduce the floatability of coal-pyrite selectively and remove the pyrite in coal,it is very important to study the exist- ing style of carbon atom on the coal-pyrite surface and the mechanism between carbon atom and hydrophobicity. The wetting heat and carbon element content of mineral-pyrite and coal-pyrite were compared by the microcalorimeter and Scanning Electron Microscope. The experiment results showed that the wetting heat of coal-pyrite was bigger and the carbon element content of carbonaceous substance were higher than the mineral-pyrite generally. With the first-princi- ple method of density functional theory ( DFT) and the plane-wave ultrasoft pseudopotential method,the adsorption process of water on the perfect pyrite surface and surface adsorbed by carbon atom was simulated. And the adsorption energy,bond Mulliken population,electron density and density of states were calculated and discussed. The simulation results showed that compared with the perfect pyrite surface,the adsorption energy on the surface adsorbed by carbon atom was positive. The surface adsorbed by carbon atom became hydrophilic. The simulation results were consistent with the results of wetting heat. The mechanism of the influence of carbon atom’s adsorption on coal-pyrite hydropho- bicity was revealed from the view of quantum chemistry.