Abstract: In order to remove the pyrite in coal,it is very important to study the existing style of carbon in the coal py- rite and the mechanism between the crystal lattice defects and floatability. The pyrite and coal pyrite in the typical mining area of China were taken as the research object. Advanced instruments were used to analyse the element,min- eral composition and surface properties. The research results show that it exists carbon impurities on the coal pyrite surface. Based on the first principle method of density functional theory (DFT),the effects of carbon impurities on the coal pyrite surface was calculated and discussed by applying the plane wave ultrasoft pseudopotential method. The sim- ulation result shows that the hydrophilism of coal pyrite bearing carbon impurities weakens,the floatability strengthens and it is easier to float. And the contact angle and flotation experiment were done and their results are consistent with the simulation. The mechanism of the relation between the lattice and its floatability was revealed from the view of quantum chemistry.