Abstract: Liquid and vapor hydrothermal upgrading of Huolinhe lignite were carried out by changing the placing meth- od of coal and water to study the effect of hydrothermal methods on the physicochemical structure and moisture reab- sorption characteristics of lignite. The experiment results showed that the dewatering and upgrading performance of va- por hydrothermal treatment was similar to that of liquid hydrothermal treatment,but the vapor hydrothermal treatment could effectively reduce the loss of organic components and increase the yield of lignite. With the increase of treatment temperature,the pore structure of the two kinds of hydrothermal upgraded coals firstly increased and then decreased, but the pore structure of vapor upgraded coals started to decrease significantly until 250 ℃ . The effect of the phase of water on the removal of oxygen containing functional groups was gradually weakened as the temperature increased, whereas the aliphatic compounds were degraded more remarkable during liquid hydrothermal upgrading. When the temperature ranged from 300 ℃ to 350 ℃ ,the moisture reabsorption characteristics of the two kinds of hydrothermal upgraded coals were obviously restrained because of the removal of oxygen containing functional groups and the shrink of pore structure. However,the engineering application prospect of vapor hydrothermal upgrading is better in considera- tion of its higher yield of solid product.