The interaction between molecular surface model fragments of lignite and water molecules trimer was studied by quantum chemistry theory. The molecular surface electrostatic potential

the reduced density gradient function(RDG) and the AIM topology of the optimized equilibrium configuration was analyzed. The results show that

the order(from high to low) of reaction activity of oxygen containing functional groups in the lignite molecule was as follows: carboxyl

hydroxyl

methoxy

methyl. Water molecules had negligible effect on electrostatic potential of the equilibrium configuration system

but they increased the maximum and minimum value point area of the electrostatic potential

and provided more active points. The adsorption reaction of water molecules and lignite surface molecular models was part of physical adsorption. The interaction between lignite and water trimer was mainly hydrogen bonding

followed by van Edward weak interaction. The hydrogen bonding between water molecules may lead to distorted deformation of the lignite molecules.