Coal-water interfacial interactions are one of the key scientific issues in clean coal technology. However, the microscopic mechanism of lignite-water interaction is still unclear in terms of atomic scale structure and electronic properties. There is a lack of systematicinvestigation on the interaction energy, stable structural features, and interaction nature of different functional groups in lignite with water molecules. Herein, the molecular mechanism of lignite-water microscopic interaction based on multi-scale molecular simulations wasinvestigated. The interaction between representative model structures of lignite and a single water molecule was investigated by quantum chemical calculations. The localized minima configurations of different adsorption sites on lignite and corresponding stable adsorption configurations are obtained. The interaction forms between lignite and water molecules were intuitively illustrated by independent gradient model ( IGM ), which mainly included van der Waals interactions and hydrogen bonds. The electrostatic interaction wasquantitatively described and identified as the dominant factor stabilizing the lignite-water interaction by energy decomposition analysis.Furthermore, the assembly behaviors and evolution characteristics of different numbers of lignite molecules interacting with a large numberof water molecules were revealed based on molecular dynamics simulations. The aggregation phenomena of lignite molecules in bulk waterwere elucidated. The molecular dynamics simulation results also confirm that lignite bind to H2O mainly through electrostatic interaction.