Abstract: The effect of humic acid, an important component of lignite, on the water content in Shengli lignite was studied. The content of oxygen containing functional groups of humic acid in Shengli lignite was determined. The isothermal adsorption and desorption curves of the lignite, brown humic acid and the residual coal were analyzed. Further the primary and secondary site adsorption of the lignite, brown humic acid and the residual coal were studied. The results show that 2/5 carboxyl and 1/5 hydroxyl in Shengli lignite are provided by humic acid. The pore size and pore volume of brown humic acid are smaller than those of the lignite. So brown humic acid is unfavorable for the formation of water clusters. The humic acid is adverse to equilibrium adsorption of water for Shengli lignite.