Abstract: In order to improve the hydrophobicity and flotability of low rank coals and realize the efficient flotation of low rank coals,the Pingshuo long-flame coal and Shengli brown coal were surface modified with three types of surfactants which are CTAB,SDS and Span-80.The oxygen-containing functional groups in each modified coal were detected through ion exchange method,and the attachment probability of them were measured as well.The modifying rule of surfactants on low rank coals were analyzed and the mechanism was also discussed.It was found that the content of oxygen-containing functional groups was the most important factor that affected the hydrophobicity and flotability of low rank coals.The modification of low rank coals with surfactants could mask part of the oxygen-containing functional groups and improve the hydrophobicity of low rank coals as well as its attachment probability on bubbles.Hydrogen bonding is the main factor that make surfactants attach on the coal surface.The functional groups on the polar end of the surfactants and the strength of the hydrogen bond between them and the oxygen-containing functional groups on the coal surface play a decisive role in the surface modification.