Abstract: The influences of hydrothermal dewatering（HTD） performed at different temperatures on the gasification characteristics of typical lignites with different metamorphic grades in China were investigated in this paper. Results show that the upgrading process significantly decreases the inherent moisture at a maximum degree of 87.31% and oxygen content,and increases calorific value and fixed carbon content.According to the oxygen/carbon ratio parameter, the coal rank increases. The complex changes occurred on coal structure during the HTD process lead to pore size of coal char develop to the microporous region, and the surface area and volume increase at first but then decrease. Due to the development of coal structure and the increment of coal rank, the gasification process of upgraded coal is delayed towards high temperature region, the temperature increases when carbon conversion rate reaches 50%. From the results of kinetic calculation, activation energy increases after the hydrothermal treatment, and the reaction order of mechanistic model is changed. Besides, all the changes caused by HTD are more obvious when the upgraded temperature increases from 250 ℃ to 300 ℃ and when the rank of raw brown coal is lower.