Abstract: In order to study the storage pattern of mositure in lignite, the adsorption mechanism of water polymer on lignite molecular surface was studied by density functional theory. Adsorption energy, Reduced density gradient(RDG), Atoms in Molecule(AIM) and Energy decomposition analysis(EDA) of the optimized adsorption configurations were calculated. The results show that: water polymer adsorbed on lignite molecular surface mainly via hydrogen bond, and van der Waals forces make little contribution to the adsorption. Carboxyl and hydroxyl functional group in lignite provide the primary adsorption sites. More hydrogen bonds formed between water polymer and lignite molecule, and adsorption energy of water polymer on lignite is larger than that of single water. Water molecule adsorbed on lignite to form equilibrium configuration under the effect of repulsive and attractive interaction, and electrostatic interaction plays a dominant role in the attractive interactions.