Abstract: The macro-qualities of coal have been explained completely. But its micro-qualities need to be studied. The electric charge distribution on the surface of coal was calculated by means of quantum chemistry. The mechanism that polymers are adsorbed on coal surface is analyzed in detail, which successfully explains why anionic polymers are adsorbed by coal surface with negative charge. Because it uneven electron density in distribution, some area of electron density is thinner on the coal surface. So the active group of polymer could be adsorbed on it by means of van der Wauls and hydrogen bond force.